Switch testing to Xena testing runtime
Switch testing to Xena testing runtime

Updating the tetsing template to Xena testing runtime:
https://governance.openstack.org/tc/reference/runtimes/xena.html

Change-Id: I2e110291242568875937b10c2b13cb138af23ba7

openstack/python-ironicclient,openstack/python-ironicclient