Add Python3 xena unit tests
Add Python3 xena unit tests

This is an automatically generated patch to ensure unit testing
is in place for all the of the tested runtimes for xena.

See also the PTI in governance [1].

[1]: https://governance.openstack.org/tc/reference/project-testing-interface.html

Change-Id: I3a42ec28f6c4a2de874b83a1f0230c12fec5cea1

openstack/mistral-dashboard,openstack/mistral-dashboard,openstack/mistral-dashboard