Fix up the bootdev recipe to rely exclusively on sysfs to find our
boot device.

This code goes to great lengths to make sure that things do not get
confused by SCSI WWN identifiers.

Also include code to make GRUB also try to install our root fs device.
This code may be nonfunctional due to glitches in the debian installer code.
Add in LVM metadata zapping, and make walk_node_through more panicky.
Merge pull request #141 from VictorLowther/pull-req-release-mesa-1.6-master-98263bd30c9272dc9a56660fb15a5b74f0cb5685

Pulling at Arkady's request.