Define self.client in MessagingCore

Currently self.client is referenced within MessagingCore,
but no definition is made in its constructor. Additionally
self.client is defined in children classes of MessagingCore.
This patchset defines self.client in the constructor of
MessagingCore and removes the redefinition in its children.

-self.client lazily loaded

Co-Authored-By: v-francoise <Vincent.FRANCOISE@b-com.com>
Change-Id: I14525a175bf1ebde3d2636024ad2f2219c79d6e1
Closes-Bug: #1521636

watcher/applier/workflow_engine/base.py

@@ -62,8 +62,8 @@ class BaseWorkFlowEngine(object):
         ev.data = {}
         payload = {'action_uuid': action.uuid,
                    'action_state': state}
-        self.applier_manager.topic_status.publish_event(ev.type.name,
-                                                        payload)
+        self.applier_manager.status_topic_handler.publish_event(
+            ev.type.name, payload)
 
     @abc.abstractmethod
     def execute(self, actions):