Python3.6/3.7 are deleted in testing runtime
Python3.6/3.7 are deleted in testing runtime

Python3.6 and Python3.7 are no longer supported by zed cycle tests, and Python3.9 was added when Python3.6 and Python3.7 were removed.

Change-Id: Ie3f0da2775b59df8d01e560b4e507cd331948ae7

openstack/sahara,openstack/sahara