Use Tempest compatible version for xenial node job

Tempest is py3 only now and xenial node has py3.5.
We tried to install the py3.6 on xenial node via devstack
but revert that solution. Later we did pin the Tempest
with compatible version on xenial which is 23.0.0

- https://github.com/openstack/devstack/blob/8cd4e9a9076e05974ed1242ccab3391c55c7070c/stackrc#L316

Change-Id: I78e184c6cb2b1448ef243766a20072baa869d1b3
1 file changed