Googling the pertinent text from the above long error:
duplicate key value violates unique constraint "name_server_pkey"
led me to this bug report:
https://bugzilla.redhat.com/show_bug.cgi?id=1530944
and the discovery I had a duplicate DNS IP address in /etc/resolv.conf
Removing this and adding the host again worked :-)
But it shouldn't have been this hard to install oVirt. May I suggest tolarance of
duplicate DNS IPs be added?
In above bug report, Yaniv Kaul says won't fix because it's user error. Perhaps,
but the oVirt installer should do a modicum of hand-holding IMO.