systemd: vdsmd: fixed sanlock requirement

Added missing .service.

Change-Id: Ic1f4270ec1db959cae458ee7292175ea8efc57b6
Signed-off-by: Sandro Bonazzola <sbonazzo@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/19572
Reviewed-by: Antoni Segura Puimedon <asegurap@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>