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: I63198ad06c1ce0ed4e6580582b269fe69842fed8
Closes-Bug: #1755102

manifests/db/sync.pp

@@ -34,6 +34,7 @@ class ec2api::db::sync (
       Anchor['ec2api::dbsync::begin']
     ],
     notify      => Anchor['ec2api::dbsync::end'],
+    tag         => 'openstack-db',
   }
 
 }

releasenotes/notes/openstack_db_tag-bdc29046cc947ea5.yaml

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

spec/classes/ec2api_db_sync_spec.rb

@@ -20,6 +20,7 @@ describe 'ec2api::db::sync' do
             'Anchor[ec2api::dbsync::begin]'
           ],
           :notify      => 'Anchor[ec2api::dbsync::end]',
+          :tag         => 'openstack-db',
         }
 
         it { is_expected.to compile.with_all_deps }