Added tag for just policy override reconfiguration

When you change policy on a running system, you expect that
this operation will be fast enough and only change policy.json
Without this tag you have to run whole role.

Use tag: nova-policy-override to just override policy.json

Added nova-config and services restart to the same task

Change-Id: I973658b6a7a7be9f836c603c39d5b11836761d5d

tasks/nova_post_install.yml

@@ -87,6 +87,13 @@
     dest: "/etc/nova/policy.json"
   when:
     - nova_policy_overrides != {}
+  notify:
+    - Manage LB
+    - Restart nova services
+    - Restart uwsgi services
+  tags:
+    - nova-config
+    - nova-policy-override
 
 # NOTE(cloudnull): This is using "cp" instead of copy with a remote_source
 #                  because we only want to copy the original files once. and we