Switch openstack-python3-zed-jobs
Switch openstack-python3-zed-jobs

In Zed, we have dropped the python 3.6/3.7[1] testing
and its support. Removing the py36 centos8 job as well as
updating the python classifier also to reflect the same.

[1] https://governance.openstack.org/tc/reference/runtimes/zed.html

Change-Id: I96076a685482d01ed095803ff716de06afd01816

openstack/sahara,openstack/sahara