[krbdev.mit.edu #1284] rcp tests and ipv6

[Ken Raeburn via RT]

The test suite support for rcp doesn't handle ipv6, nor does it handle
output from rcp saying that connections were refused at the first
address tried but there are other addresses to try.

If the local hostname maps to an ipv6 address as well as an ipv4
address, this combination can cause false negative results from the
test suite.

I suggest fixing both:

 - make the standalone daemon code handle ipv6 if available

 - make the test suite deal with multiple listed addresses when some
   are refusing connections, timing out, whatever (this one might also
   affect, say, disconnected laptops with their "normal" addresses
   listed in /etc/hosts but not on any interface while disconnected)