oo-accept-broker, oo-register-dns: unauth'd DNS

oo-accept-broker: Use the same logic as the openshift-origin-dns-nsupdate
plug-in to determine which authentication mechanism is used, and correctly
test DNS using unauthenticated updates if the plug-in is so configured.

oo-register-dns: Attempt an unauthenticated update if the user does not
indicate to use Kerberos or a keyfile and there is no keyfile at the
default location.
Merge pull request #3767 from Miciah/bug-1015255-oo-accept-broker-and-oo-register-dns-unauthenticated-DNS-updates

Merged by openshift-bot