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: I79c078e5945c45090cdb53959f3e87d2d7e18081
Closes-Bug: #1755102

manifests/db/sync.pp

@@ -30,6 +30,7 @@ class ceilometer::db::sync(
       Anchor['ceilometer::dbsync::begin']
     ],
     notify      => Anchor['ceilometer::dbsync::end'],
+    tag         => 'openstack-db',
   }
 
 }

releasenotes/notes/openstack_db_tag-874ef77468c5d1f2.yaml

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

spec/classes/ceilometer_db_sync_spec.rb

@@ -17,6 +17,7 @@ describe 'ceilometer::db::sync' do
                          'Anchor[ceilometer::config::end]',
                          'Anchor[ceilometer::dbsync::begin]'],
         :notify      => 'Anchor[ceilometer::dbsync::end]',
+        :tag         => 'openstack-db',
       )
     end
 
@@ -39,6 +40,7 @@ describe 'ceilometer::db::sync' do
                          'Anchor[ceilometer::config::end]',
                          'Anchor[ceilometer::dbsync::begin]'],
         :notify      => 'Anchor[ceilometer::dbsync::end]',
+        :tag         => 'openstack-db',
       )
       }
     end