drop support for V1 VTN API

Change-Id: I87e91785edc7890aeda6c078a80c6c05ab6af66b
diff --git a/xos/synchronizer/steps/sync_port_addresses.py b/xos/synchronizer/steps/sync_port_addresses.py
index 37d8dc6..b3a7837 100644
--- a/xos/synchronizer/steps/sync_port_addresses.py
+++ b/xos/synchronizer/steps/sync_port_addresses.py
@@ -39,6 +39,8 @@
         if vtn_service.vtnAPIVersion >= 2:
             logger.info("skipping SyncPortAddresses due to VTN API Version")
             return
+        else:
+            raise Exception("VTN API Version 1 is no longer supported by VTN Synchronizer")
 
         # build up a dictionary of port-->[wan_addrs] mappings
         port_addrs = {}