Merge from oslo-incubator for notifier

Goal: merge from oslo-incubator change  I282d4ae3311bc3fcda6be8e5a1fceecfc8ddb115

Done via:
python update.py --nodeps --base nova --dest-dir ../nova --modules notifier

Change-Id: I5ed80458f1073d6e5185e2769eed85a49dec5d10
Merge "Merge from oslo-incubator for notifier"