Prevent is_subrecord iterating past the domain name itself.
Prevent is_subrecord iterating past the domain name itself.

Change-Id: I828f3ec6064e45c3428e96ce4c4fb8ead8827abf

kiall/designate-py3,openstack/designate,richm/designate,tonyli71/designate,grahamhayes/designate,cneill/designate,ramsateesh/designate,muraliselva10/designate,melodous/designate,cneill/designate,cneill/designate-testing,kiall/designate-py3,kiall/designate-py3,cneill/designate,cneill/designate,ionrock/designate,tonyli71/designate,cneill/designate-testing,grahamhayes/designate,cneill/designate-testing,muraliselva10/designate,openstack/designate,melodous/designate,grahamhayes/designate,richm/designate,kiall/designate-py3,ramsateesh/designate,muraliselva10/designate,cneill/designate,ionrock/designate,openstack/designate,ionrock/designate,tonyli71/designate,kiall/designate-py3,ramsateesh/designate,melodous/designate,NeCTAR-RC/designate,melodous/designate,NeCTAR-RC/designate