Add support code for multicast DNS service discovery
To simplify standalone configuration, we need an ability for IPA
to discovery ironic and ironic-inspector on the local network.
This change adds the support code for using multicast DNS (RFC 6762)
with DNS service discovery (RFC 6763) to publish and discover
OpenStack services as proposed in the API SIG guideline
This commit is a follow-up of "switch to using stestr"
which was merged already .
After switch to using stestr, testrepository is unnecessary
and should be removed.