Modify member methods in kamaki.cli.cmds classes

Refs: #9

Renamed:
kamaki.cli.cmds._optional_json: _print --> print_
kamaki.cli.cmds.cyclades.Wait: _wait --> wait
kamaki.cli.cmds.cyclades.ServerWait: _wait --> wait
kamaki.cli.cmds.image: _load_image_meta --> load_image_meta
kamak.cli.cmds.network: _wait --> wait
kamaki.cli.cmds.pithos.PithosAccount:
    _is_dir --> obj_is_dir
    _resolve_pithos_url --> resolve_pithos_url

Removed:
kamaki.cli.cmds.pithos.PithosAccount:
    _validate_image_meta, _validate_image_location