Add Python 3 Train unit tests
Add Python 3 Train unit tests

This is a mechanically generated patch to ensure unit testing is in place
for all of the Tested Runtimes for Train.

See the Train python3-updates goal document for details:
https://governance.openstack.org/tc/goals/train/python3-updates.html

Change-Id: I87be8b97790f73256e9b26b9756b5e8a2461314d
Story: #2005924
Task: #34223

openstack/monasca-notification,openstack/monasca-notification