I'm not sure how much of the original analysis was right.  I've just fired up a network-less Windows VM and 'localhost' seems to resolve just fine:

>>> socket.gethostbyname('localhost')
'127.0.0.1'
>>> socket.getaddrinfo('localhost', 80, socket.AF_UNSPEC, socket.SOCK_STREAM)

[(<AddressFamily.AF_INET6: 23>,
  <SocketKind.SOCK_STREAM: 1>,
  0,
  '',
  ('::1', 80, 0, 0)),
 (<AddressFamily.AF_INET: 2>,
  <SocketKind.SOCK_STREAM: 1>,
  0,
  '',
  ('127.0.0.1', 80))]


But we should defer to our Windows experts on this.

(also, perhaps we should simply mandate that buildbots have at least basic DNS functionality. This would lighten the maintenance load on the test suite slightly.)