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.
* Remove unused user agrument from backend.get_snapshot().
* Various typo fixes.