A bit meh, but we *need* hardcoded addresses in these tests, because
we can't get them from a running coredns. These may be in-use and this
fails the tests then. Do an ugly err.Error() string match if this is the
case to prevent failing the test for something not in our control.

A better fix would be to retreive the listening address from coredns via
some api, so we could listen on :0 for these as well. No such API exists
as of yet.