Comment 1 for bug 1569790

Need to add such check into Nailgun (NetworkCheck class). Now we have partial validation here: NetworkCheck.neutron_check_l3_addresses_not_match_subnet_and_broadcast but it does not cover this case.
There should also be a check for intersection with gateways (one is set in Neutron L3 and another is added in case of using multiple node groups).