Added retries for db_sync

If db sync fails, it is never retried leading to errors. So, this
patch adds retries for db_sync to avoid sync fails.

Change-Id: Iba2b099c917762ed45192f374d8b67e26ec3664a
Closes-Bug: #1628580

manifests/db/sync.pp

@@ -16,6 +16,8 @@ class mistral::db::sync {
     user        => 'mistral',
     logoutput   => on_failure,
     refreshonly => true,
+    try_sleep   => 5,
+    tries       => 10,
   }
 
   Exec['mistral-db-sync'] -> Exec['mistral-db-populate']