specification->package fails on manifest entries with specific outputs,
resulting in an invalid home configuration. This changes the import command
to use specification->package+output instead.
* guix/scripts/home/import.scm (manifest+configuration-files->code): Make sure
manifest entries with specific output are also handled.
* tests/home-import.scm: Specify output in home environment manifest entry.
Signed-off-by: Ludovic Courtès <ludo@gnu.org>
