hsm: encapsulate path in appropriateDevice

As a continuation of Ie0d4d805ca333990ea1f612eb03a87f4a505f4a8,
appropriateDevice method now returns 'path' as well.

Change-Id: Iaf8f53999bde70eb4b2b1b0a927c9412d4597134
Signed-off-by: Daniel Erez <derez@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/24406
Reviewed-by: Federico Simoncelli <fsimonce@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>
Reviewed-by: Nir Soffer <nsoffer@redhat.com>