Override _create_stream() in TCPClient.

        Tornado 4.5 added the kwargs 'source_ip' and 'source_port'.
        Due to this, use **kwargs to swallow these and any future
        kwargs to maintain compatibility.

def _create_stream(self, max_buffer_size, af, addr, **kwargs):  # pylint: disable=unused-argument
        '''
        Override _create_stream() in TCPClient.

        Tornado 4.5 added the kwargs 'source_ip' and 'source_port'.
        Due to this, use **kwargs to swallow these and any future
        kwargs to maintain compatibility.
        '''
        # Always connect in plaintext; we'll convert to ssl if necessary
        # after one connection has completed.
        sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
        _set_tcp_keepalive(sock, self.opts)
        stream = tornado.iostream.IOStream(
            sock,
            max_buffer_size=max_buffer_size)
        if tornado.version_info < (5,):
            return stream.connect(addr)
        return stream, stream.connect(addr)