Allowed Address Pair API Tests Enhancements

Add test to update 'allowed-address-pair' attribute of port

-Create a port without allowed-address-pair
-Set allowed-address-pair attribute of port using port_update
-Validate that allowed-address-pair attribute of port is updated successfully

Change-Id: I0556617f837f62e3ccc06f50c049af0b227357b0
Merge "Allowed Address Pair API Tests Enhancements"