services: nix: Point Nix to bin/bash.
The nix-service-type will create the nix.conf file pointing to
`bin/sh' file in the bash-minimal package, however this is a symbolic
link to `bin/bash' in that same package, so when the sandbox gets
created there will be a symlink in the Nix sandbox like this:
drwxr-xr-x 2 nobody nogroup 4096 Sep 18 13:10 .
drwxr-x--- 10 nobody nixbld 4096 Sep 18 13:10 ..
lrwxrwxrwx 1 nobody nogroup 4 Jan 1 1970 sh -> bash
Making builds that depend on /bin/sh fail since /bin/bash does not
exist in the sandbox.
* gnu/services/nix.scm (nix-service-etc): Change ‘build-sandbox-paths’ to
point to ‘bin/bash’.
Change-Id: I9138e9b772b8468382cfde6d133f0758837d03ff
Signed-off-by: Ludovic Courtès <ludo@gnu.org>