server: Skip unnecessary installation of separate packages

Currently both neutron-server and separate service packages are
installed regardless of the services actually used. However this is
quite redundant especially when only neutron-server is used in CentOS.

Skip installation of separate packages when the monolithic server
service is requested.

Change-Id: I72359a2e78c57de57722d01b4c16c0db85189f54

manifests/server.pp

@@ -332,6 +332,7 @@ class neutron::server (
     'DEFAULT/enable_default_route_bfd':         value => $enable_default_route_bfd;
   }
 
+  if $service_name {
     if $server_package {
       package { 'neutron-server':
         ensure => $package_ensure,
@@ -339,7 +340,7 @@ class neutron::server (
         tag    => ['openstack', 'neutron-package'],
       }
     }
-
+  } else {
     if $api_package_name {
       package { 'neutron-api':
         ensure => $package_ensure,
@@ -355,6 +356,7 @@ class neutron::server (
         tag    => ['openstack', 'neutron-package'],
       }
     }
+  }
 
   if ($auth_strategy == 'keystone') {
     include neutron::keystone::authtoken