'Return a single metadata item.'

def show(self, req, snapshot_id, id):

    context = req.environ['cinder.context']
    data = self._get_metadata(context, snapshot_id)
    try:
        return {'meta': {id: data[id]}}
    except KeyError:
        raise exception.SnapshotMetadataNotFound(snapshot_id=snapshot_id, metadata_key=id)
