[show priority-group drop counters] Remove backup with cached PG drop…

… counters after 'config reload' (#2386)

#### What I did
After config reload for some period of time when COUNTERS_PG_PORT_MAP is not created yet, CLI command 'show prioriy-group counter' exits with the traceback because it expects COUNTERS_PG_PORT_MAP to be present and doesn't do proper handling for the situation when it is not yet populated.
Handling was fixed

#### How I did it
use "not" instead of "is None"

#### How to verify it
UT added

#### Previous command output (if the output of a command-line utility has changed)
```
root@r-lionfish-13:/home/admin# show priority-group drop counters
Traceback (most recent call last):
  File "/usr/local/bin/pg-drop", line 262, in <module>
    main()
  File "/usr/local/bin/pg-drop", line 255, in main
    pgdropstat.print_all_stat(COUNTER_TABLE_PREFIX, "pg_drop" )
  File "/usr/local/bin/pg-drop", line 160, in print_all_stat
    self.build_header(type)
  File "/usr/local/bin/pg-drop", line 119, in build_header
    single_key = list(header_map.keys())[0]
IndexError: list index out of range

```

#### New command output (if the output of a command-line utility has changed)

`COUNTERS_PORT_NAME_MAP is empty!`

scripts/pg-drop

@@ -58,15 +58,15 @@ class PgDropStat(object):
                 Get port ID using object ID
             """
             port_id = self.counters_db.get(self.counters_db.COUNTERS_DB, COUNTERS_PG_PORT_MAP, oid)
-            if port_id is None:
-                print("Port is not available for oid '{}'".format(oid), file=sys.stderr)
+            if not port_id:
+                print("Port is not available for oid '{}'".format(oid))
                 sys.exit(1)
             return port_id
 
         # Get all ports
         self.counter_port_name_map = self.counters_db.get_all(self.counters_db.COUNTERS_DB, COUNTERS_PORT_NAME_MAP)
-        if self.counter_port_name_map is None:
-            print("COUNTERS_PORT_NAME_MAP is empty!", file=sys.stderr)
+        if not self.counter_port_name_map:
+            print("COUNTERS_PORT_NAME_MAP is empty!")
             sys.exit(1)
 
         self.port_pg_map = {}
@@ -78,8 +78,8 @@ class PgDropStat(object):
 
         # Get PGs for each port
         counter_pg_name_map = self.counters_db.get_all(self.counters_db.COUNTERS_DB, COUNTERS_PG_NAME_MAP)
-        if counter_pg_name_map is None:
-            print("COUNTERS_PG_NAME_MAP is empty!", file=sys.stderr)
+        if not counter_pg_name_map:
+            print("COUNTERS_PG_NAME_MAP is empty!")
             sys.exit(1)
 
         for pg in counter_pg_name_map:
@@ -101,8 +101,8 @@ class PgDropStat(object):
             oid - object ID for entry in redis
         """
         pg_index = self.counters_db.get(self.counters_db.COUNTERS_DB, COUNTERS_PG_INDEX_MAP, oid)
-        if pg_index is None:
-            print("Priority group index is not available for oid '{}'".format(table_id), file=sys.stderr)
+        if not pg_index:
+            print("Priority group index is not available for oid '{}'".format(oid))
             sys.exit(1)
         return pg_index
 
@@ -111,7 +111,7 @@ class PgDropStat(object):
             Construct header for table with PG counters
         """
         if pg_drop_type is None:
-            print("Header info is not available!", file=sys.stderr)
+            print("Header info is not available!")
             sys.exit(1)
 
         self.header_list = ['Port']

tests/pgdrop_input/counters_db.json

@@ -0,0 +1,83 @@
+{
+    "COUNTERS_PORT_NAME_MAP": {
+    },
+    "COUNTERS_PG_NAME_MAP": {
+        "Ethernet0:0": "oid:0x1a00000000034f",
+        "Ethernet0:1": "oid:0x1a000000000350",
+        "Ethernet0:2": "oid:0x1a000000000351",
+        "Ethernet0:3": "oid:0x1a000000000352",
+        "Ethernet0:4": "oid:0x1a000000000353",
+        "Ethernet0:5": "oid:0x1a000000000354",
+        "Ethernet0:6": "oid:0x1a000000000355",
+        "Ethernet0:7": "oid:0x1a000000000356",
+        "Ethernet4:0": "oid:0x1a000000000377",
+        "Ethernet4:1": "oid:0x1a000000000378",
+        "Ethernet4:2": "oid:0x1a000000000379",
+        "Ethernet4:3": "oid:0x1a00000000037a",
+        "Ethernet4:4": "oid:0x1a00000000037b",
+        "Ethernet4:5": "oid:0x1a00000000037c",
+        "Ethernet4:6": "oid:0x1a00000000037d",
+        "Ethernet4:7": "oid:0x1a00000000037e",
+        "Ethernet8:0": "oid:0x1a00000000039f",
+        "Ethernet8:1": "oid:0x1a0000000003a0",
+        "Ethernet8:2": "oid:0x1a0000000003a1",
+        "Ethernet8:3": "oid:0x1a0000000003a2",
+        "Ethernet8:4": "oid:0x1a0000000003a3",
+        "Ethernet8:5": "oid:0x1a0000000003a4",
+        "Ethernet8:6": "oid:0x1a0000000003a5",
+        "Ethernet8:7": "oid:0x1a0000000003a6"
+     },
+    "COUNTERS_PG_PORT_MAP": {
+        "oid:0x1a00000000034f": "oid:0x1000000000012",
+        "oid:0x1a000000000350": "oid:0x1000000000012",
+        "oid:0x1a000000000351": "oid:0x1000000000012",
+        "oid:0x1a000000000352": "oid:0x1000000000012",
+        "oid:0x1a000000000353": "oid:0x1000000000012",
+        "oid:0x1a000000000354": "oid:0x1000000000012",
+        "oid:0x1a000000000355": "oid:0x1000000000012",
+        "oid:0x1a000000000356": "oid:0x1000000000012",
+        "oid:0x1a000000000377": "oid:0x1000000000013",
+        "oid:0x1a000000000378": "oid:0x1000000000013",
+        "oid:0x1a000000000379": "oid:0x1000000000013",
+        "oid:0x1a00000000037a": "oid:0x1000000000013",
+        "oid:0x1a00000000037b": "oid:0x1000000000013",
+        "oid:0x1a00000000037c": "oid:0x1000000000013",
+        "oid:0x1a00000000037d": "oid:0x1000000000013",
+        "oid:0x1a00000000037e": "oid:0x1000000000013",
+        "oid:0x1a00000000039f": "oid:0x1000000000014",
+        "oid:0x1a0000000003a0": "oid:0x1000000000014",
+        "oid:0x1a0000000003a1": "oid:0x1000000000014",
+        "oid:0x1a0000000003a2": "oid:0x1000000000014",
+        "oid:0x1a0000000003a3": "oid:0x1000000000014",
+        "oid:0x1a0000000003a4": "oid:0x1000000000014",
+        "oid:0x1a0000000003a5": "oid:0x1000000000014",
+        "oid:0x1a0000000003a6": "oid:0x1000000000014"
+    },
+
+    "COUNTERS_PG_INDEX_MAP": {
+        "oid:0x1a00000000034f": "0",
+        "oid:0x1a000000000350": "1",
+        "oid:0x1a000000000351": "2",
+        "oid:0x1a000000000352": "3",
+        "oid:0x1a000000000353": "4",
+        "oid:0x1a000000000354": "5",
+        "oid:0x1a000000000355": "6",
+        "oid:0x1a000000000356": "7",
+        "oid:0x1a000000000377": "0",
+        "oid:0x1a000000000378": "1",
+        "oid:0x1a000000000379": "2",
+        "oid:0x1a00000000037a": "3",
+        "oid:0x1a00000000037b": "4",
+        "oid:0x1a00000000037c": "5",
+        "oid:0x1a00000000037d": "6",
+        "oid:0x1a00000000037e": "7",
+        "oid:0x1a00000000039f": "0",
+        "oid:0x1a0000000003a0": "1",
+        "oid:0x1a0000000003a1": "2",
+        "oid:0x1a0000000003a2": "3",
+        "oid:0x1a0000000003a3": "4",
+        "oid:0x1a0000000003a4": "5",
+        "oid:0x1a0000000003a5": "6",
+        "oid:0x1a0000000003a6": "7"
+    }
+}

tests/pgdrop_input/counters_db2.json

@@ -0,0 +1,63 @@
+{
+    "COUNTERS_PORT_NAME_MAP": {
+        "Ethernet0": "oid:0x1000000000012",
+        "Ethernet4": "oid:0x1000000000013",
+        "Ethernet8": "oid:0x1000000000014"
+
+    },
+    "COUNTERS_PG_NAME_MAP": {
+     },
+    "COUNTERS_PG_PORT_MAP": {
+        "oid:0x1a00000000034f": "oid:0x1000000000012",
+        "oid:0x1a000000000350": "oid:0x1000000000012",
+        "oid:0x1a000000000351": "oid:0x1000000000012",
+        "oid:0x1a000000000352": "oid:0x1000000000012",
+        "oid:0x1a000000000353": "oid:0x1000000000012",
+        "oid:0x1a000000000354": "oid:0x1000000000012",
+        "oid:0x1a000000000355": "oid:0x1000000000012",
+        "oid:0x1a000000000356": "oid:0x1000000000012",
+        "oid:0x1a000000000377": "oid:0x1000000000013",
+        "oid:0x1a000000000378": "oid:0x1000000000013",
+        "oid:0x1a000000000379": "oid:0x1000000000013",
+        "oid:0x1a00000000037a": "oid:0x1000000000013",
+        "oid:0x1a00000000037b": "oid:0x1000000000013",
+        "oid:0x1a00000000037c": "oid:0x1000000000013",
+        "oid:0x1a00000000037d": "oid:0x1000000000013",
+        "oid:0x1a00000000037e": "oid:0x1000000000013",
+        "oid:0x1a00000000039f": "oid:0x1000000000014",
+        "oid:0x1a0000000003a0": "oid:0x1000000000014",
+        "oid:0x1a0000000003a1": "oid:0x1000000000014",
+        "oid:0x1a0000000003a2": "oid:0x1000000000014",
+        "oid:0x1a0000000003a3": "oid:0x1000000000014",
+        "oid:0x1a0000000003a4": "oid:0x1000000000014",
+        "oid:0x1a0000000003a5": "oid:0x1000000000014",
+        "oid:0x1a0000000003a6": "oid:0x1000000000014"
+    },
+
+    "COUNTERS_PG_INDEX_MAP": {
+        "oid:0x1a00000000034f": "0",
+        "oid:0x1a000000000350": "1",
+        "oid:0x1a000000000351": "2",
+        "oid:0x1a000000000352": "3",
+        "oid:0x1a000000000353": "4",
+        "oid:0x1a000000000354": "5",
+        "oid:0x1a000000000355": "6",
+        "oid:0x1a000000000356": "7",
+        "oid:0x1a000000000377": "0",
+        "oid:0x1a000000000378": "1",
+        "oid:0x1a000000000379": "2",
+        "oid:0x1a00000000037a": "3",
+        "oid:0x1a00000000037b": "4",
+        "oid:0x1a00000000037c": "5",
+        "oid:0x1a00000000037d": "6",
+        "oid:0x1a00000000037e": "7",
+        "oid:0x1a00000000039f": "0",
+        "oid:0x1a0000000003a0": "1",
+        "oid:0x1a0000000003a1": "2",
+        "oid:0x1a0000000003a2": "3",
+        "oid:0x1a0000000003a3": "4",
+        "oid:0x1a0000000003a4": "5",
+        "oid:0x1a0000000003a5": "6",
+        "oid:0x1a0000000003a6": "7"
+    }
+}

tests/pgdrop_input/counters_db3.json

@@ -0,0 +1,62 @@
+{
+    "COUNTERS_PORT_NAME_MAP": {
+        "Ethernet0": "oid:0x1000000000012",
+        "Ethernet4": "oid:0x1000000000013",
+        "Ethernet8": "oid:0x1000000000014"
+    },
+    "COUNTERS_PG_NAME_MAP": {
+        "Ethernet0:0": "oid:0x1a00000000034f",
+        "Ethernet0:1": "oid:0x1a000000000350",
+        "Ethernet0:2": "oid:0x1a000000000351",
+        "Ethernet0:3": "oid:0x1a000000000352",
+        "Ethernet0:4": "oid:0x1a000000000353",
+        "Ethernet0:5": "oid:0x1a000000000354",
+        "Ethernet0:6": "oid:0x1a000000000355",
+        "Ethernet0:7": "oid:0x1a000000000356",
+        "Ethernet4:0": "oid:0x1a000000000377",
+        "Ethernet4:1": "oid:0x1a000000000378",
+        "Ethernet4:2": "oid:0x1a000000000379",
+        "Ethernet4:3": "oid:0x1a00000000037a",
+        "Ethernet4:4": "oid:0x1a00000000037b",
+        "Ethernet4:5": "oid:0x1a00000000037c",
+        "Ethernet4:6": "oid:0x1a00000000037d",
+        "Ethernet4:7": "oid:0x1a00000000037e",
+        "Ethernet8:0": "oid:0x1a00000000039f",
+        "Ethernet8:1": "oid:0x1a0000000003a0",
+        "Ethernet8:2": "oid:0x1a0000000003a1",
+        "Ethernet8:3": "oid:0x1a0000000003a2",
+        "Ethernet8:4": "oid:0x1a0000000003a3",
+        "Ethernet8:5": "oid:0x1a0000000003a4",
+        "Ethernet8:6": "oid:0x1a0000000003a5",
+        "Ethernet8:7": "oid:0x1a0000000003a6"
+     },
+    "COUNTERS_PG_PORT_MAP": {
+    },
+
+    "COUNTERS_PG_INDEX_MAP": {
+        "oid:0x1a00000000034f": "0",
+        "oid:0x1a000000000350": "1",
+        "oid:0x1a000000000351": "2",
+        "oid:0x1a000000000352": "3",
+        "oid:0x1a000000000353": "4",
+        "oid:0x1a000000000354": "5",
+        "oid:0x1a000000000355": "6",
+        "oid:0x1a000000000356": "7",
+        "oid:0x1a000000000377": "0",
+        "oid:0x1a000000000378": "1",
+        "oid:0x1a000000000379": "2",
+        "oid:0x1a00000000037a": "3",
+        "oid:0x1a00000000037b": "4",
+        "oid:0x1a00000000037c": "5",
+        "oid:0x1a00000000037d": "6",
+        "oid:0x1a00000000037e": "7",
+        "oid:0x1a00000000039f": "0",
+        "oid:0x1a0000000003a0": "1",
+        "oid:0x1a0000000003a1": "2",
+        "oid:0x1a0000000003a2": "3",
+        "oid:0x1a0000000003a3": "4",
+        "oid:0x1a0000000003a4": "5",
+        "oid:0x1a0000000003a5": "6",
+        "oid:0x1a0000000003a6": "7"
+    }
+}

tests/pgdrop_input/counters_db4.json

@@ -0,0 +1,62 @@
+{
+    "COUNTERS_PORT_NAME_MAP": {
+        "Ethernet0": "oid:0x1000000000012",
+        "Ethernet4": "oid:0x1000000000013",
+        "Ethernet8": "oid:0x1000000000014"
+    },
+    "COUNTERS_PG_NAME_MAP": {
+        "Ethernet0:0": "oid:0x1a00000000034f",
+        "Ethernet0:1": "oid:0x1a000000000350",
+        "Ethernet0:2": "oid:0x1a000000000351",
+        "Ethernet0:3": "oid:0x1a000000000352",
+        "Ethernet0:4": "oid:0x1a000000000353",
+        "Ethernet0:5": "oid:0x1a000000000354",
+        "Ethernet0:6": "oid:0x1a000000000355",
+        "Ethernet0:7": "oid:0x1a000000000356",
+        "Ethernet4:0": "oid:0x1a000000000377",
+        "Ethernet4:1": "oid:0x1a000000000378",
+        "Ethernet4:2": "oid:0x1a000000000379",
+        "Ethernet4:3": "oid:0x1a00000000037a",
+        "Ethernet4:4": "oid:0x1a00000000037b",
+        "Ethernet4:5": "oid:0x1a00000000037c",
+        "Ethernet4:6": "oid:0x1a00000000037d",
+        "Ethernet4:7": "oid:0x1a00000000037e",
+        "Ethernet8:0": "oid:0x1a00000000039f",
+        "Ethernet8:1": "oid:0x1a0000000003a0",
+        "Ethernet8:2": "oid:0x1a0000000003a1",
+        "Ethernet8:3": "oid:0x1a0000000003a2",
+        "Ethernet8:4": "oid:0x1a0000000003a3",
+        "Ethernet8:5": "oid:0x1a0000000003a4",
+        "Ethernet8:6": "oid:0x1a0000000003a5",
+        "Ethernet8:7": "oid:0x1a0000000003a6"
+     },
+    "COUNTERS_PG_PORT_MAP": {
+        "oid:0x1a00000000034f": "oid:0x1000000000012",
+        "oid:0x1a000000000350": "oid:0x1000000000012",
+        "oid:0x1a000000000351": "oid:0x1000000000012",
+        "oid:0x1a000000000352": "oid:0x1000000000012",
+        "oid:0x1a000000000353": "oid:0x1000000000012",
+        "oid:0x1a000000000354": "oid:0x1000000000012",
+        "oid:0x1a000000000355": "oid:0x1000000000012",
+        "oid:0x1a000000000356": "oid:0x1000000000012",
+        "oid:0x1a000000000377": "oid:0x1000000000013",
+        "oid:0x1a000000000378": "oid:0x1000000000013",
+        "oid:0x1a000000000379": "oid:0x1000000000013",
+        "oid:0x1a00000000037a": "oid:0x1000000000013",
+        "oid:0x1a00000000037b": "oid:0x1000000000013",
+        "oid:0x1a00000000037c": "oid:0x1000000000013",
+        "oid:0x1a00000000037d": "oid:0x1000000000013",
+        "oid:0x1a00000000037e": "oid:0x1000000000013",
+        "oid:0x1a00000000039f": "oid:0x1000000000014",
+        "oid:0x1a0000000003a0": "oid:0x1000000000014",
+        "oid:0x1a0000000003a1": "oid:0x1000000000014",
+        "oid:0x1a0000000003a2": "oid:0x1000000000014",
+        "oid:0x1a0000000003a3": "oid:0x1000000000014",
+        "oid:0x1a0000000003a4": "oid:0x1000000000014",
+        "oid:0x1a0000000003a5": "oid:0x1000000000014",
+        "oid:0x1a0000000003a6": "oid:0x1000000000014"
+    },
+
+    "COUNTERS_PG_INDEX_MAP": {
+    }
+}