Yet another issue with pg_upgrade vs unix_socket_directories

I went back for another try at building the Fedora packages with 9.2
branch tip ... and it still failed at pg_upgrade's "make check".
The reason for this is that test.sh starts a couple of random
postmasters, and those postmasters expect to put their sockets in
the configured default location (which is now /var/run/postgresql
on Fedora), and that's not there in a minimal build environment.

I hacked it up with the attached quick-and-dirty patch, but I wonder
if anyone's got a better idea.

regards, tom lane