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: I9a47da537d9f1554271cb8e1e7284a98d364313c
Closes-Bug: #1628580

manifests/db/sync.pp

@@ -19,6 +19,8 @@ class nova::db::sync(
   exec { 'nova-db-sync':
     command     => "/usr/bin/nova-manage ${extra_params} db sync",
     refreshonly => true,
+    try_sleep   => 5,
+    tries       => 10,
     logoutput   => on_failure,
     subscribe   => [
       Anchor['nova::install::end'],