Code review comment for lp:~raharper/curtin/trunk.fix-lp1722322

Can you just add a comment that 'wipe_volume' is potentially destructive to partitions that start at very beginnning of disk or end at very end.

something like:
  # wipe_volume wipes 1M at front and end of the disk. That could
  # destroy partition's filesystem data that lived there.

other than that, i approve.

Unless you wanted to make a generic helper for prepping disks with an arbitrary storage config.