docker: use noop_resource for Nova_cell_v2

Per puppet-nova commit 2c743a6bff5b17a85d1e0500f3a9ecb21468204e
there is now a custom resource for Nova_cell_v2 configuration.
As this resource runs automatically regardless of our use
of puppet tags we need to explicitly disable it to be able to
generate Nova API configs for docker.

Change-Id: Id675dc124464acddc3fc5a88b017a351e93ba685
Closes-bug: #1681841

docker/services/nova-api.yaml

@@ -50,7 +50,10 @@ outputs:
           - get_attr: [NovaApiBase, role_data, config_settings]
           - apache::default_vhost: false
       step_config: &step_config
-        get_attr: [NovaApiBase, role_data, step_config]
+        list_join:
+          - "\n"
+          - - "['Nova_cell_v2'].each |String $val| { noop_resource($val) }"
+            - {get_attr: [NovaApiBase, role_data, step_config]}
       service_config_settings: {get_attr: [NovaApiBase, role_data, service_config_settings]}
       # BEGIN DOCKER SETTINGS
       puppet_config: