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.