Connect to statsd via TCP and return the IOStream handle.
        :rtype: iostream.IOStream

def _tcp_socket(self):
        """Connect to statsd via TCP and return the IOStream handle.
        :rtype: iostream.IOStream
        """
        sock = iostream.IOStream(socket.socket(
                    socket.AF_INET, socket.SOCK_STREAM, socket.IPPROTO_TCP))
        sock.connect(self._address, self._tcp_on_connected)
        sock.set_close_callback(self._tcp_on_closed)
        return sock