Deprecate auth_version option

The same option in tempest was deprecated by [1], because Identity v3
API is the only available version now. Deprecate the option and remove
the old logic to support Identity v2 API which was already removed.

[1] https://review.opendev.org/c/openstack/tempest/+/906158

Change-Id: Id12672fabfd51755eeff7b0d701abfb63e0abce0
3 files changed