Drop auth and corresponding unit tests

auth has been migrated to tempest-lib.
Fix all auth imports to use tempest-lib. Drop auth and related
unit tests.
Use token client from tempest-lib as well.

Depends-on: Ie6435b4f3a367b0a8cec68f21c0b4f5f61d6b688
Change-Id: I8c2772d9fb42d352f4a1d3e74e20ce6e8f483559
13 files changed