Check for undefined _oslomsg_rpc variables

Some services may make use of notifications but do not require rpc
messaging and have the _oslomsg_rpc variables undefined.

Update the when clauses on the tasks configuring RabbitMQ for
notifications to ignore undefined '_oslomsg_rpc_vhost' and
'_oslomsg_rpc_userid' variables.

Change-Id: I96e59b98e069bffb30c0d1851f777aa6b891f14f

sync/tasks/mq_setup.yml

@@ -67,7 +67,8 @@
         name: "{{ _oslomsg_notify_vhost }}"
         state: "present"
       when:
-        - _oslomsg_notify_vhost != _oslomsg_rpc_vhost
+        - (_oslomsg_rpc_vhost is undefined) or
+          (_oslomsg_notify_vhost != _oslomsg_rpc_vhost)
 
     - name: Apply Notify RabbitMQ vhost policies
       rabbitmq_policy:
@@ -78,7 +79,8 @@
         vhost: "{{ _oslomsg_notify_vhost }}"
       loop: "{{ _oslomsg_notify_policies | default([]) + oslomsg_notify_policies }}"
       when:
-        - _oslomsg_notify_vhost != _oslomsg_rpc_vhost
+        - (_oslomsg_rpc_vhost is undefined) or
+          (_oslomsg_notify_vhost != _oslomsg_rpc_vhost)
 
     - name: Add Notify RabbitMQ user
       rabbitmq_user:
@@ -92,7 +94,8 @@
         force: true
       no_log: true
       when:
-        - _oslomsg_notify_userid != _oslomsg_rpc_userid
+        - (_oslomsg_rpc_userid is undefined) or
+          (_oslomsg_notify_userid != _oslomsg_rpc_userid)
 
 - name: Setup RPC MQ Service (Qdrouterd)
   delegate_to: "{{ _oslomsg_rpc_setup_host }}"