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: Icd2700fe8c27a647dab8d91a4f9c20eda930b4e1
Closes-Bug: #1755102
(cherry picked from commit b563459e37)

manifests/db/sync.pp

@@ -35,6 +35,6 @@ class keystone::db::sync(
       Anchor['keystone::dbsync::begin']
     ],
     notify      => Anchor['keystone::dbsync::end'],
-    tag         => 'keystone-exec',
+    tag         => ['keystone-exec', 'openstack-db']
   }
 }

releasenotes/notes/openstack_db_tag-89916b8b22f8e4a5.yaml

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

spec/classes/keystone_db_sync_spec.rb

@@ -18,6 +18,7 @@ describe 'keystone::db::sync' do
                           'Anchor[keystone::config::end]',
                           'Anchor[keystone::dbsync::begin]'],
           :notify      => 'Anchor[keystone::dbsync::end]',
+          :tag         => ['keystone-exec', 'openstack-db'],
         )
       }
     end
@@ -43,6 +44,7 @@ describe 'keystone::db::sync' do
                           'Anchor[keystone::config::end]',
                           'Anchor[keystone::dbsync::begin]'],
           :notify      => 'Anchor[keystone::dbsync::end]',
+          :tag         => ['keystone-exec', 'openstack-db'],
         )
       }
     end