hammer2 - Add 'info' and 'mountall' directives

hammer2 - Add 'info' and 'mountall' directives

* hammer2 info - scans all block devices with hammer2 partitions and
  displays available super-root entries.

* hammer2 mountall - scans all block devices with hammer2 partitions
  and mounts their @LOCAL PFS in /var/hammer2/LOCAL.serno.s%d%c
  in the background, waiting until the mounts complete or 15 seconds
  without a status change.

  The idea here is to bring all local block devices online, allowing
  all PFS's related to the H2 block devices to become active (mounting
  one makes them all available), but still giving the system operator
  the ability to idle a block device for maintenance by dismounting
  all of its actively-mounted PFSs.

  A bit confusing, the feature will be ironed out later.