* VERSION_REGEX = re.compile('\d+-\d+-\d+')
   might as well make that '\d{4}-\d{2}-\d{2}'
 * METADATA_NETWORK_KEY = 'content_path'
   really, this is more than 'network' related.
   any time binary data is needed, it is just referenced by its 'content_path'.
   this is also used for user-data (or 'files' too)

   some info on that:
   http://people.canonical.com/~smoser/config-drive-v2/README.txt
 * urlhelper / http_client
   should urlhelper just set up:
      urlhelper.status_codes.CONFLICT = http_client.CONFLICT