pithos: Bulk deletion enhancement.

Bulk delete operations (delete container contents &
massively delete objects under a specific object path)
used to issue the quota change for each object deletion separately.

This commit introduces the following enhancement:
the backend computes the total quota change for the account/project and
contacts the quota holder component only once (at the end of the whole
procedure).
cyclades: Minor bug fix in pprint_network

* Print 'None' if a network doesn't belong to any users instead of
crashing.
cyclades: Update snf-manage argument names

* Update various snf-manage commands to use --display-mails instead of
--displayname.
* Add --display-mails option in port-inspect.
cyclades: Bug fixes in volume related commands

* Add a check to both name length and disk template length in
snf-manage volume-type-create.
* Add a check to name length of snapshots.
* Add a generic try/except clause to handle Pithos responses.
* Add --user/--public options in snapshot-show/image-show.
* Add a boolean "snapshot" field in image-list.
* Remove unused user agrument from backend.get_snapshot().
* Remove --wait option from snapshot-create.
* Various typo fixes.