fix: admin and member gates are broken

The patrole-admin and patrole-member gates are broken because they
are trying to test a policy action ('os_compute_api:os-services') that
was changed in the Ussuri release. This commit adds a new policy feature
flag so that this policy test is backwards compatible.

Change-Id: Ia80279ae8ffcc17f10bed05338c41d0c23eea063
diff --git a/patrole_tempest_plugin/config.py b/patrole_tempest_plugin/config.py
index 5eab0e3..b087148 100644
--- a/patrole_tempest_plugin/config.py
+++ b/patrole_tempest_plugin/config.py
@@ -189,7 +189,12 @@
                 default=True,
                 help="""Is the cloud running the Train release or newer? If
 so, the Keystone Trust API is enforced differently depending on passed
-arguments""")
+arguments"""),
+    cfg.BoolOpt('changed_nova_policies_ussuri',
+                default=True,
+                help="""Are the Nova API policies available in the
+cloud (e.g. os_compute_api:os-services)? These policies were
+changed in Ussuri.""")
 ]
 
 
diff --git a/patrole_tempest_plugin/tests/api/compute/test_services_rbac.py b/patrole_tempest_plugin/tests/api/compute/test_services_rbac.py
index dd7a4c3..da4923d 100644
--- a/patrole_tempest_plugin/tests/api/compute/test_services_rbac.py
+++ b/patrole_tempest_plugin/tests/api/compute/test_services_rbac.py
@@ -14,11 +14,19 @@
 #    under the License.
 
 from tempest.common import utils
+from tempest import config
 from tempest.lib import decorators
 
 from patrole_tempest_plugin import rbac_rule_validation
 from patrole_tempest_plugin.tests.api.compute import rbac_base
 
+CONF = config.CONF
+
+if CONF.policy_feature_enabled.changed_nova_policies_ussuri:
+    _OS_COMPUTE_API_OS_SERVICES = "os_compute_api:os-services:list"
+else:
+    _OS_COMPUTE_API_OS_SERVICES = "os_compute_api:os-services"
+
 
 class ServicesRbacTest(rbac_base.BaseV2ComputeRbacTest):
 
@@ -31,7 +39,7 @@
 
     @rbac_rule_validation.action(
         service="nova",
-        rules=["os_compute_api:os-services"])
+        rules=[_OS_COMPUTE_API_OS_SERVICES])
     @decorators.idempotent_id('7472261b-9c6d-453a-bcb3-aecaa29ad281')
     def test_list_services(self):
         with self.override_role():