bundles/postgresql: make sure we have postgres_role before adding postgres_db

bundles/postgresql/items.py

@@ -41,6 +41,7 @@ for database, config in node.metadata.get('postgresql', {}).get('databases', {})
     postgres_dbs[database] = {
         'owner': config['owner'],
         'needs': {
+            'postgres_role:',
             'svc_systemd:postgresql',
         },
     }