Refactored Watcher objects to use OVO

In this changeset, I modified all existing Watcher objects to now
rely on oslo.versionedobjects as a base.

Change-Id: I3c9b1ca6da529d128743b99020350f28926ea1a2
Partially-Implements: blueprint watcher-versioned-objects

watcher/api/controllers/v1/audit.py

@@ -519,7 +519,7 @@ class AuditsController(rest.RestController):
         audit_dict = audit.as_dict()
 
         new_audit = objects.Audit(context, **audit_dict)
-        new_audit.create(context)
+        new_audit.create()
 
         # Set the HTTP Location Header
         pecan.response.location = link.build_url('audits', new_audit.uuid)