work-around for dual container share access rockstor#94

Rockstor forces unique share allocation, however
- bareos-webui-php-fpm needs /var/www/html on web-data
but web-data is populated by bareos-webui: and
- bareos-webui populates web-data via /usr/share/bareos-webui
Plus, bareos-webui requires bareos-webui-php-fpm so the later
must start before the former.

Have bareos-webui-php-fpm establish bareos-webui volumes, and
add share duplicate mount it requires via opts -v. Working around
Rockstor repeate share use limitation. Then have bareos-webui
inherit via opts (--volumes-from bareos-webui-php-fpm) all 3 volumes.
Only two of which it is required to share with it's php-fpm counterpart.
We assume no side effects from: "/mnt2/bareos-webui-data:/var/www/html"
applied via inheritance within bareos-webui container.

Currently, requires dictating a share name !!

bareos-server-set.json

@@ -158,15 +158,21 @@
         "tag": "latest",
         "launch_order": 4,
         "volumes": {
+          "/usr/share/bareos-webui": {
+            "description": "BareOS 'WebUI' data Share.",
+            "label": "'WebUI' data [must be bareos-webui-data]"
+          },
           "/etc/bareos-webui": {
             "description": "BareOS 'WebUI' configuration Share.",
             "label": "'WebUI' config [e.g. bareos-webui-config]"
-          },
-          "/usr/share/bareos-webui": {
-            "description": "BareOS 'WebUI' data Share.",
-            "label": "'WebUI' data [e.g. bareos-webui-data]"
           }
-        }
+        },
+        "opts": [
+          [
+            "-v",
+            "/mnt2/bareos-webui-data:/var/www/html"
+          ]
+        ]
       },
       "bareos-webui": {
         "image": "barcus/bareos-webui",