Ensure token refresh. Fixes bug 1044316.

FAIL of test
  Request to list user's roles without a valid token should fail
used to be causing ERROR of
  Remove a role assigned to a user on a tenant

Solved by ensuring that this FAIL has no side-effects.

Change-Id: Ide5849f70aab26e2af2a52ed83371da9c51bf5d7
diff --git a/tempest/tests/identity/admin/test_roles.py b/tempest/tests/identity/admin/test_roles.py
index 4256da5..813f64a 100644
--- a/tempest/tests/identity/admin/test_roles.py
+++ b/tempest/tests/identity/admin/test_roles.py
@@ -237,10 +237,12 @@
         (user, tenant, role) = self._get_role_params()
         token = self.client.get_auth()
         self.client.delete_token(token)
-        self.assertRaises(exceptions.Unauthorized,
-                          self.client.list_user_roles, tenant['id'],
-                          user['id'])
-        self.client.clear_auth()
+        try:
+            self.assertRaises(exceptions.Unauthorized,
+                              self.client.list_user_roles, tenant['id'],
+                              user['id'])
+        finally:
+            self.client.clear_auth()
 
     def test_list_user_roles_for_non_existent_user(self):
         """Attempt to list roles of a non existent user should fail"""