CORD-2865 get creator from subscriber object

Change-Id: I51bc8841ff1802949336849c79366cf10993ca4b
diff --git a/xos/synchronizer/model_policies/model_policy_vsgserviceinstance.py b/xos/synchronizer/model_policies/model_policy_vsgserviceinstance.py
index 050093f..6800e81 100644
--- a/xos/synchronizer/model_policies/model_policy_vsgserviceinstance.py
+++ b/xos/synchronizer/model_policies/model_policy_vsgserviceinstance.py
@@ -106,14 +106,17 @@
         assert (slice is not None)
         assert (node is not None)
         assert (desired_image is not None)
-        assert (service_instance.creator is not None)
         assert (node.site_deployment.deployment is not None)
         assert (desired_image is not None)
 
+        assert(service_instance.volt)
+        assert(service_instance.volt.subscriber)
+        assert(service_instance.volt.subscriber.creator)
+
         instance = Instance(slice=slice,
                             node=node,
                             image=desired_image,
-                            creator=service_instance.creator,
+                            creator=service_instance.volt.subscriber.creator,
                             deployment=node.site_deployment.deployment,
                             flavor=flavors[0],
                             isolation=slice.default_isolation,