Allow installing tempest only with keystone

Modify the lib/tempest to not fail
 if no nova or glance available.

* This allows performance test of keystone and neutron with
  tempest (or tempest stress runner) without having system
  noise from another components.
* Depending on not required components for tempest is bad practice,
  tempest service decorators expected to allow tempest,
  to run in more minimal system out-of-the-box.

Change-Id: Ifc40b1eb5c4b79d96a5fae919b88afecca642ca0
fix python-* lib from git installation

We're using all the magic variables based on python-fooclient, however
all the inline code was using fooclient for variables. So we had a
mismatch, which was kindly pointed out by some of the 3rd party ci
testers.

Change-Id: I27a56222c7e8e610fba8bf97672d2a42f5cf14ca
Merge "Allow installing tempest only with keystone"
Merge "fix python-* lib from git installation"
Merge branch 'master' of https://github.com/openstack-dev/devstack