partially fix users page - Python 3 style sorted() rockstor#2564

"cmp" sorted parameter and builtin function dropped
in Python 3.
Partial fix as only Admin users showing - suspect unrelated
issue.

src/rockstor/storageadmin/views/ug_helpers.py

@@ -77,9 +77,7 @@ def combined_users():
     for u in User.objects.all():
         if u.username not in uname_list:
             users.append(u)
-    return sorted(
-        users, cmp=lambda x, y: cmp(x.username.lower(), y.username.lower())  # noqa F821
-    )
+    return sorted(users, key=lambda each: each.username.lower())
 
 
 def combined_groups():
@@ -97,7 +95,4 @@ def combined_groups():
     for g in Group.objects.all():
         if g.groupname not in gname_list:
             groups.append(g)
-    return sorted(
-        groups,
-        cmp=lambda x, y: cmp(x.groupname.lower(), y.groupname.lower()),  # noqa F821
-    )
+    return sorted(groups, key=lambda each: each.groupname.lower())