Add optional dependency mysql -> neutron-server

In cases where neutron server is on the same node
as mysqld it is desirable to have the database
running before the service.

Change-Id: I0a6c3a1d6481b4250a0a948c3e5a14e5a0a5e7de

manifests/db/mysql.pp

@@ -24,7 +24,7 @@
       charset      => $charset,
       collate      => $collate,
       require      => Class['mysql::server'],
-    }
+    } -> Service <| title == 'neutron-server' |>
   } else {
     require mysql::python