Takes the advantage of already symlinks created on /dev/disk/by-label/ by
60-persistent-storage.rules add by udev hook.

Tested on:
* Real machine as CD-ROM and USB key drive.
* KVM as CD-ROM and DISK (for both modes, in combination with IDE and SCSI)
* VirtualBox as IDE CD-ROM.

IMPORTANT note: Since isohybrid is a hack, if more partitions are added to
USB key drive, filesystem on these partitions MUST have LABEL, otherwise
USB key will fail to boot. Anyway there is an option archisodevice=,
to force and specific device where live-media reside.
(Maybe isohybrid will change the hack method used in a future)

More info at:
http://mailman.archlinux.org/pipermail/arch-releng/2010-March/000890.html
http://mailman.archlinux.org/pipermail/arch-releng/2010-March/000913.html

Signed-off-by: Gerardo Exequiel Pozzi <vmlinuz386@yahoo.com.ar>