Use openstack-python3-train-jobs for python3 test runtime
Use openstack-python3-train-jobs for python3 test runtime

Depends-On:https://review.opendev.org/#/c/641878/

Change-Id: I8e3120f54bbf43271d126abe3b788f0d1ab29f03

openstack/python-mistralclient,openstack/python-mistralclient