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
diff --git a/tempest/common/cred_provider.py b/tempest/common/cred_provider.py
index 3223027..461097f 100644
--- a/tempest/common/cred_provider.py
+++ b/tempest/common/cred_provider.py
@@ -16,8 +16,8 @@
 
 from oslo_log import log as logging
 import six
+from tempest_lib import auth
 
-from tempest import auth
 from tempest import config
 from tempest import exceptions