Add audit.planner events

In this changeset, I implemented the following notifications:

- audit.planner.start
- audit.planner.end
- audit.planner.error

Partially Implements: blueprint audit-versioned-notifications-api

Change-Id: I29d371f8cb3fd7948c87bec97186e24a88e8fdb6

watcher/objects/fields.py

@@ -127,8 +127,9 @@ class NotificationAction(BaseWatcherEnum):
     DELETE = 'delete'
 
     STRATEGY = 'strategy'
+    PLANNER = 'planner'
 
-    ALL = (CREATE, UPDATE, EXCEPTION, DELETE, STRATEGY)
+    ALL = (CREATE, UPDATE, EXCEPTION, DELETE, STRATEGY, PLANNER)
 
 
 class NotificationPriorityField(BaseEnumField):