Add 'openstack-db' tag to db-sync Exec resource

In order to make easy orchestration on all OpenStack db-sync, add this
tag so people can use this tag in composition layer.
A use case it to set some orchestration to make sure MySQL Galera is
ready before running any Exec with this tag.

Change-Id: I8215df855b260b9421df121d136be2e77eab1346
Closes-Bug: #1755102

manifests/db/sync.pp

@@ -25,6 +25,7 @@ class aodh::db::sync (
       Anchor['aodh::dbsync::begin']
     ],
     notify      => Anchor['aodh::dbsync::end'],
+    tag         => 'openstack-db',
   }
 
 }

releasenotes/notes/openstack_db_tag-987f513d508e7717.yaml

@@ -0,0 +1,3 @@
+---
+features:
+  - Add openstack-db tag to Exec that run db-sync.

spec/classes/aodh_db_sync_spec.rb

@@ -19,6 +19,7 @@ describe 'aodh::db::sync' do
                          'Anchor[aodh::config::end]',
                          'Anchor[aodh::dbsync::begin]'],
         :notify      => 'Anchor[aodh::dbsync::end]',
+        :tag         => 'openstack-db',
       )
     end