Tempest config generator had a wrong logic for the case when there is
only one keystone version is available.
This patch uses the same urls(discovered from the catalog) for keystone
as it is done for the case when we have both keystone v2 and v3.
Also, it reverts I1c28dbcdc69b0510a2a9de67e6af7160123932fd
Change-Id: I44dbcb9650e22f8867709f3d0fb5f39ef2ce477a