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: I836b56d125ec781f24b5ea1797ac882b353e2379
Closes-Bug: #1628580

manifests/db/sync.pp

@@ -21,6 +21,8 @@ class neutron::db::sync(
     command     => "neutron-db-manage ${extra_params} upgrade heads",
     path        => '/usr/bin',
     refreshonly => true,
+    try_sleep   => 5,
+    tries       => 10,
     logoutput   => on_failure,
     subscribe   => [
       Anchor['neutron::install::end'],