Improve exception that is raised following invalid service

This patchset changes the exception that is raised following
an invalid service being passed in for testing. Instead of
a NotFound getting raised (which doesn't make sense), the
original exception, RbacInvalidServiceException, is raised
instead. In addition "Exception" is appended to the original
exception name for greater clarity and consistency with other
exception names.

This patchset is similar to [0] which aims to simplify and
consolidate how service input is validated.

[0] https://review.openstack.org/#/c/577963/

Change-Id: Ib91a6581f89a528630d756840176b0e16663fa6f
diff --git a/patrole_tempest_plugin/policy_authority.py b/patrole_tempest_plugin/policy_authority.py
index b813f88..3339a5d 100644
--- a/patrole_tempest_plugin/policy_authority.py
+++ b/patrole_tempest_plugin/policy_authority.py
@@ -136,7 +136,7 @@
 
         if not service or service not in cls.available_services:
             LOG.debug("%s is NOT a valid service.", service)
-            raise rbac_exceptions.RbacInvalidService(
+            raise rbac_exceptions.RbacInvalidServiceException(
                 "%s is NOT a valid service." % service)
 
     @classmethod