udev can create the temporary node for us now. (On bootup we don't
know where a writable filesystem is mounted). Also the parent handling
is not needed anymore, cause udev is able to pass us the node name
of the parent device.
Here is a update to extras/volume_id/*
o The device is now specified by the DEVPATH in the environment,
it's no longer needed to pass the major/minor to the callout.
o leading spaces and slashes are now removed from the returned string
and spaces are replaced by underscore, to not to confuse udev.
o Arnd Bergmann <arnd@arndb.de> provided the code to recognize s390
dasd disk labels. The -d switch tries to read the main block device
instead of the partition.
