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/common/messaging/messaging_handler.py

@@ -110,7 +110,6 @@ class MessagingHandler(threading.Thread):
 
     def stop(self):
         LOG.debug('Stopped server')
-        self.__server.wait()
         self.__server.stop()
 
     def publish_event(self, event_type, payload, request_id=None):