[SEBA-218] Making ONU serial number handling case insensitive

Change-Id: I7cd42041709c5e8041959da84c7e1853a8ba0636
diff --git a/xos/synchronizer/model_policies/model_policy_att_workflow_driver_serviceinstance.py b/xos/synchronizer/model_policies/model_policy_att_workflow_driver_serviceinstance.py
index ef3363b..26b0367 100644
--- a/xos/synchronizer/model_policies/model_policy_att_workflow_driver_serviceinstance.py
+++ b/xos/synchronizer/model_policies/model_policy_att_workflow_driver_serviceinstance.py
@@ -67,7 +67,7 @@
 
             subscriber = None
             try:
-                subscriber = RCORDSubscriber.objects.get(onu_device=si.serial_number)
+                subscriber = [s for s in RCORDSubscriber.objects.all() if s.onu_device.lower() == si.serial_number.lower()][0]
             except IndexError:
                 # we just want to find out if it exists or not
                 pass