Fix the check of tempest_roles parameter

Change-Id: I57fb7e040dece7a3cc724bdebe3eac9d72f010dd
Related-PROD: PROD-23947
diff --git a/tungsten_tempest_plugin/tests/api/contrail/rbac_base.py b/tungsten_tempest_plugin/tests/api/contrail/rbac_base.py
index 2685c39..8b92d5b 100644
--- a/tungsten_tempest_plugin/tests/api/contrail/rbac_base.py
+++ b/tungsten_tempest_plugin/tests/api/contrail/rbac_base.py
@@ -110,7 +110,7 @@
         super(BaseContrailTest, cls).skip_checks()
         if not CONF.service_available.contrail:
             raise cls.skipException("Contrail support is required")
-        if CONF.auth.tempest_roles != ['admin']:
+        if "admin" not in CONF.auth.tempest_roles:
             raise cls.skipException(
                 "%s skipped because tempest roles is not admin" % cls.__name__)