Udev rules don't handle multiple CDROM devices correctly

[Matthew Burgess]

See the above URL for details. Basically if a system has more than one CDROM drive, only the last one detected will get the /dev/cdrom symlink. In addition to this, we don't appear to handle DVD drives similarly. Do we want to? If so, I'd rather we build the 'cdrom_id' helper and use that to correctly determine drive capabilities (see the gentoo rules in the udev tarball for example usage).