Implemented audit.update notification

In this changeset, I implemented the sending of update notifications
whenever an audit is modified.

Change-Id: I5ccc2516ce896ae7d4ef542b133e8f052eaed602
Partially-Implements: blueprint audit-versioned-notifications-api

watcher/tests/db/utils.py

@@ -75,7 +75,6 @@ def get_test_audit(**kwargs):
         'strategy_id': kwargs.get('strategy_id', None),
         'scope': kwargs.get('scope', []),
     }
-
     # ObjectField doesn't allow None nor dict, so if we want to simulate a
     # non-eager object loading, the field should not be referenced at all.
     if kwargs.get('goal'):