Start libvirt after installing it

The libvirt service needs startup scripts installed by the package
before it can start, so make sure the package is installed first.

Change-Id: I2d03f50a8d633b2d7a273736857da8fe46593a37

manifests/compute/libvirt.pp

@@ -191,6 +191,7 @@ class nova::compute::libvirt (
     enable   => true,
     name     => $libvirt_service_name,
     provider => $::nova::params::special_service_provider,
+    require  => Package['libvirt'],
   }
 
   nova_config {