Prefer ID_SERIAL over ID_SERIAL_SHORT (#1138254)

While there are devices that export multiple block devices with the same
ID_SERIAL_SHORT (e.g. card readers) they use different ID_SERIAL values for
those block devices. Using ID_SERIAL_SHORT instead of ID_SERIAL results in all
the card reader's block devices being considered "obvious multipath devices"
where multipathd lost the race condition game and didn't assemble them
correctly. Which is terribly wrong.