Hey,

When reconfiguring recently, I ran in to issues with the Guix Data
Service and probably the Patchwork service too.

Looking at the change, I think it's clear there's a problem, because
some system tests were changed, and I'm guessing they were changed so
that they passed [1].

1: https://git.savannah.gnu.org/cgit/guix.git/commit/?id=6c0679215f4ffa534c1eb2e8c8a6e043a0c993fe

Passing tests are good, but working around real issues in tests is not,
because that means that the situation outside of the tests can break and
if it does, the test result is misleading.

Patchwork, the Guix Data Service and maybe other things currently depend
on the default behaviour of PostgreSQL to find the socket. Given that
the service now uses a different (non-default) value, they don't
work.

One workaround, the one employed in the tests is to revert to the old
behaviour for the PostgreSQL service by setting socket-directory to #f.