Configure uri_v3 auth url

Keystone v3 endpoint is enabled by default in the overcloud,
so we shall configure it in tempest.

Because of bug 1295132 a uri_v3 has to be defined anyways
for tempest to run.

Change-Id: I2bbe258a6f008bacd1847c71acb073e81a822af7
Merge "Configure uri_v3 auth url"