Add Action Notification

This patch set adds the following action notifications:

- action.create
- action.update
- action.delete
- action.execution.start
- action.execution.end
- action.execution.error

Partially Implements: blueprint action-versioned-notifications-api

Change-Id: If0bc25bfb7cb1bff3bfa2c5d5fb9ad48b0794168

watcher/common/exception.py

@@ -182,6 +182,10 @@ class EagerlyLoadedActionPlanRequired(InvalidActionPlan):
     msg_fmt = _("Action plan %(action_plan)s was not eagerly loaded")
 
 
+class EagerlyLoadedActionRequired(InvalidActionPlan):
+    msg_fmt = _("Action %(action)s was not eagerly loaded")
+
+
 class InvalidUUID(Invalid):
     msg_fmt = _("Expected a uuid but received %(uuid)s")