Move RbacAuthority class into separate module

This patchset simply moves the RbacAuthority abstract base class
into its own module for better code organization.

Change-Id: I89bee142671645f304d622b9e6c25fbab745a7e2
diff --git a/patrole_tempest_plugin/policy_authority.py b/patrole_tempest_plugin/policy_authority.py
index 99348b9..25dcea6 100644
--- a/patrole_tempest_plugin/policy_authority.py
+++ b/patrole_tempest_plugin/policy_authority.py
@@ -24,8 +24,8 @@
 from tempest.common import credentials_factory as credentials
 from tempest import config
 
+from patrole_tempest_plugin.rbac_authority import RbacAuthority
 from patrole_tempest_plugin import rbac_exceptions
-from patrole_tempest_plugin.rbac_utils import RbacAuthority
 
 CONF = config.CONF
 LOG = logging.getLogger(__name__)