Add pass-through support for tempest element

Introduce support for pass-through on tempest.conf.

Change-Id: I89be1374407d75f09aad08ca4981c4b855b3c0c9
Pin setuptools to <8.0

Setuptools 8.0 changed the way it parses version strings and many of our
openstack packages break when using it. Pinning this for now until our
packages are fixed.

Closes-Bug: #1402305

Change-Id: If3300a6b1ef1c633fc339f884e9dab0d82bc0720
Merge "Add pass-through support for tempest element"