Fix dsvm gate failure

Tempest module 'auth' was moved into tempest-lib repo, this change
caused import error, that was fixed in this commit.

Change-Id: I8b93a9ce47cc24afe9b4f52fbc78de79a42b7fa8
(cherry picked from commit c6b536e5d0)

mistral/tests/functional/base.py

@@ -17,10 +17,10 @@ import mock
 import os
 import time
 
-from tempest import auth
 from tempest import clients
 from tempest import config
 from tempest import test as test
+from tempest_lib import auth
 from tempest_lib.common import rest_client
 from tempest_lib import exceptions