Ensure mDNS TCP/UDP threads service unhandled exceptions
Ensure mDNS TCP/UDP threads service unhandled exceptions

Change-Id: I304fae07c3b83c48e152ac2e8600ff214d1d8a0f
Closes-Bug: 1443453

muraliselva10/designate,kiall/designate-py3,cneill/designate,muraliselva10/designate,openstack/designate,grahamhayes/designate,grahamhayes/designate,kiall/designate-py3,openstack/designate,cneill/designate-testing,kiall/designate-py3,tonyli71/designate,cneill/designate-testing,cneill/designate,cneill/designate,tonyli71/designate,grahamhayes/designate,ionrock/designate,ramsateesh/designate,kiall/designate-py3,openstack/designate,muraliselva10/designate,cneill/designate,ramsateesh/designate,tonyli71/designate,cneill/designate-testing,kiall/designate-py3,ionrock/designate,cneill/designate,ionrock/designate,ramsateesh/designate