Broken list_volume_user_ids command in Syndicate Admin tool

[iychoi]

The list_volume_user_ids command in syndicate admin tool is broken. It calls a storage.list_volume_user_ids function which is non-existing.

from https://github.com/syndicate-storage/syndicate-core/blob/master/ms/common/api.py#L341

@Authenticate()
@ListAPIGuard( SyndicateUser, caller_user="caller_user", parse_args=SyndicateUser.ParseArgs )
def list_volume_user_ids( volume_name_or_id, **attrs ):
   """
   List the emails of the users that can access data
   in a given volume.  That is, which users have
   registered User Gateways that can access
   the volume's metadata.

   Positional arguments:
      volume_name (str):
         The name of the volume to query.

   Returns:
      The list of emails of users that can run User Gateways
      within this volume.

   Authorization:
      An administrator can list any Volume's user IDs.
      A user must own the Volume.
   """
   return storage.list_volume_user_ids( volume_name_or_id, **attrs )