Notification and CDM partial update

In this changeset, I implemented the notification handling (Rx only)
system for consuming incoming notifications, more especially the Nova
ones. The notifications handlers also contain the logic which
incrementally updates the Compute model.

Change-Id: Ia036a5a2be6caa64b7f180de38821b57c624300c
Partially-implements: blueprint cluster-model-objects-wrapper

watcher/applier/workflow_engine/base.py

@@ -82,8 +82,7 @@ class BaseWorkFlowEngine(loadable.Loadable):
         ev.data = {}
         payload = {'action_uuid': action.uuid,
                    'action_state': state}
-        self.applier_manager.status_topic_handler.publish_event(
-            ev.type.name, payload)
+        self.applier_manager.publish_status_event(ev.type.name, payload)
 
     @abc.abstractmethod
     def execute(self, actions):