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: I0f54a3b753137e6dbc5ea0c3a77886ad622422d7

openstack/python-designateclient