Recent commits have integrated Archipelago v2 mapfiles to Pithos. This
commit updates Cyclades to go along with the recent changes in Pithos.
Specifically, this commit makes the following changes:

* Use the 'mapfile' attribute of the Pithos objects, instead of the old 'hash'
  attribute. Also, this attribute needs no custom prefixing
  ('archip:' or 'pithos:').
* Do not store 'is_snapshot' and 'status' attributes as plankton
  properties. The 'is_snapshot' attribute is now provided from Pithos.
  Also, the 'status' attribute can be derived from the 'available'
  attribute.
* Remove code from 'snf-dispatcher' that used to update the 'status'
  plankton property when the OP_INSTANCE_SNAPSHOT Ganeti job completed.
  This functionality is now covered internally from Pithos.