'Delete a keypair
:param key: The :class:`Keypair` (or its ID) to delete.
:param user_id: Id of key-pair owner (Admin only).
:returns: An instance of novaclient.base.TupleWithMeta'

@api_versions.wraps('2.10')
def delete(self, key, user_id=None):

    query_string = (('?user_id=%s' % user_id) if user_id else '')
    url = ('/%s/%s%s' % (self.keypair_prefix, base.getid(key), query_string))
    return self._delete(url)
