luna-prefs: Inherit webos_machine_dep

* it's writting MACHINE to ${sysconfdir}/prefs/properties/machineName

Open-webOS-DCO-1.0-Signed-off-by: Martin Jansa <martin.jansa@lge.com>
Change-Id: I0946b7b1a643b850214cb7e17a067440823a0cea
Reviewed-on: https://g2g.palm.com/1850
Reviewed-by: Build Verification
Reviewed-by: Martin Jansa <Martin.Jansa@lge.com>
Tested-by: Martin Jansa <Martin.Jansa@lge.com>
Reviewed-by: Susan Montooth <susan.montooth@lge.com>