Fixesguix/guix#1901.
Previously, ‘guix gc --list-busy’ (which is invoked by ‘guix-daemon’) would
open a connection to the daemon, which in turn attempts to create
/var/guix/profiles/per-user/$USER. However, when ‘guix-daemon‘ is running as
an unprivileged user, creating that directory fails with EPERM. Because of
this, garbage collection would always fail when running the unprivileged
daemon on Guix System.
* guix/scripts/gc.scm (guix-gc): Remove upfront call to ‘open-connection’.
Instead, use ‘with-store’ only for operations that require it.
Change-Id: I1fbfd97cf7ba9e3087f7287b4776ea2f6623400d
7445776b7e