Comment 4 for bug 1605336

When LBaaS _create_port_for_vip creates the the request body for the port here, it doesn't include the 'dns_name' attribute: https://github.com/openstack/neutron-lbaas/blob/master/neutron_lbaas/db/loadbalancer/loadbalancer_db.py#L334

If we got the port creation request from the Neutron ReST API and the DNS integration extension was enabled, the API would assign a default value to the 'dns_name' attribute if the user didn't specify it. But in this case, LBaaS is by-passing the ReST API, so when the DNS extension processes the request, we get a KeyError exception when looking for 'dns_name' in the request.