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 for the metadata 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.