CORD-2329: Add constraint to assign VMs to the same nodes as vspgwu

Change-Id: Ie8fa9afc846a88b964b07d31a3ccc9d88956acc4
diff --git a/xos/synchronizer/model_policies/model_policy_vspgwutenant.py b/xos/synchronizer/model_policies/model_policy_vspgwutenant.py
index 1f0e7d5..393491c 100644
--- a/xos/synchronizer/model_policies/model_policy_vspgwutenant.py
+++ b/xos/synchronizer/model_policies/model_policy_vspgwutenant.py
@@ -20,6 +20,7 @@
 
 class VSPGWUTenantPolicy(TenantWithContainerPolicy):
     model_name = "VSPGWUTenant"
+    constrain_by_service_instance = True
 
     def handle_create(self, service_instance):
         return self.handle_update(service_instance)