Some good and some bad news. test.winehq.org:1234 doesn't work at all, neither on Wine, it hangs everywhere (actually it even hangs on my browser waiting for reply!).
So I tried http://0.0.0.0:1234, and it fixes the other broken aspect on w8adm with about:blank, so I got rid of that hack in tests. But it still times out on a couple machines, see: https://testbot.winehq.org/JobDetails.pl?Key=138362
Then I tried a bogus url like http://www.abcd.ef, and it *still* times out on those machines: https://testbot.winehq.org/JobDetails.pl?Key=138364
So at this point I'll keep the timeout, remove the other workaround, and go with http://0.0.0.0:1234, since it seems like the best solution? Unless you have a better idea I can try. :-/