Enable tempest tests

[hertrste]

OpenStack provides an integration test suite called tempest: https://opendev.org/openstack/tempest

For OpenStack development with openstack-nix it would be very helpful to be able to run the tempest test suite conveniently.

[github-actions]

This issue is stale because it has been open for 90 days with no activity.

[phip1611]

This is still relevant I think