Replace os with os_primary

This is a trivial change that replaces os with os_primary as
os Tempest attribute is deprecated in Pike.

Change-Id: Ibb9d9ca6cfa37b92bff040310bf713e1c240a4df
diff --git a/patrole_tempest_plugin/tests/api/identity/v3/test_trusts_rbac.py b/patrole_tempest_plugin/tests/api/identity/v3/test_trusts_rbac.py
index 763c407..c25af25 100644
--- a/patrole_tempest_plugin/tests/api/identity/v3/test_trusts_rbac.py
+++ b/patrole_tempest_plugin/tests/api/identity/v3/test_trusts_rbac.py
@@ -68,7 +68,8 @@
         service="keystone",
         rule="identity:create_trust",
         extra_target_data={
-            "trust.trustor_user_id": "os.auth_provider.credentials.user_id"
+            "trust.trustor_user_id":
+            "os_primary.auth_provider.credentials.user_id"
         })
     def test_create_trust(self):
         self.rbac_utils.switch_role(self, toggle_rbac_role=True)