Skip installation of unused neutron-rpc-server

The neutron-rpc-server service is not required in case the plugin does
not require any rpc service (e.g. ml2 ovn). Skip installation of
the package in case rpc service is not requested.

Change-Id: I5d36bf8e52b52f7d1d8cbd5391a732dcde97ef42

manifests/server.pp

@@ -361,7 +361,7 @@ class neutron::server (
       }
     }
 
-    if $rpc_package_name {
+    if $rpc_package_name and $rpc_service_name {
       package { 'neutron-rpc-server':
         ensure => $package_ensure,
         name   => $rpc_package_name,