Returns a restclients.Key object for the given key ID.  If the
        key ID isn't found, or if there is an error communicating with the
        KWS, a DataFailureException will be thrown.

def get_key(self, key_id):
        """
        Returns a restclients.Key object for the given key ID.  If the
        key ID isn't found, or if there is an error communicating with the
        KWS, a DataFailureException will be thrown.
        """
        url = ENCRYPTION_KEY_URL.format(key_id)
        return self._key_from_json(self._get_resource(url))