CORD-1354 fix NetworkSlice and ControllerSite created when they already exists

Change-Id: Ic37464dac40b3e5f92b705f30337ddc77df54ac0
diff --git a/xos/synchronizer/model_policies/model_policy_Site.py b/xos/synchronizer/model_policies/model_policy_Site.py
index f800092..07fe6f3 100644
--- a/xos/synchronizer/model_policies/model_policy_Site.py
+++ b/xos/synchronizer/model_policies/model_policy_Site.py
@@ -5,9 +5,10 @@
     # make sure site has a ControllerSite record for each controller
     ctrl_sites = ControllerSite.objects.filter(site_id=site.id)
     existing_controllers = [cs.controller for cs in ctrl_sites]
+    existing_controller_ids = [c.id for c in existing_controllers]
 
     all_controllers = Controller.objects.all()
     for ctrl in all_controllers:
-        if ctrl not in existing_controllers:
+        if ctrl.id not in existing_controller_ids:
             ctrl_site = ControllerSite(controller=ctrl, site=site)
             ctrl_site.save()