Send remote command to STB.

async def send_cmd(self, cmd, loop=None):
        """Send remote command to STB."""
        _LOGGER.info("Send cmd = %s", cmd)

        if cmd not in COMMANDS and cmd not in range(0, 999):
            _LOGGER.error("Unknown command")
            raise PyMediaroomError("Unknown commands")

        keys = []
        if cmd in range(0, 999):
            for character in str(cmd):
                keys.append(COMMANDS["Number"+str(character)])
            if len(keys) < 3:
                keys.append(COMMANDS["OK"])
            self.current_channel = cmd
        else:
            keys = [COMMANDS[cmd]]

        try:
            async with timeout(OPEN_CONTROL_TIMEOUT, loop=loop):
                async with self.lock:
                    _LOGGER.debug("Connecting to %s:%s", self.stb_ip, REMOTE_CONTROL_PORT)
                    stb_recv, stb_send = await asyncio.open_connection(self.stb_ip,
                                                                       REMOTE_CONTROL_PORT,
                                                                       loop=loop)
                    await stb_recv.read(6)
                    _LOGGER.info("Connected to %s:%s", self.stb_ip, REMOTE_CONTROL_PORT)

                    for key in keys:
                        _LOGGER.debug("%s key=%s", cmd, key)
                        stb_send.write("key={}\n".format(key).encode('UTF-8'))
                        _ = await stb_recv.read(3)
                        await asyncio.sleep(0.300)

        except asyncio.TimeoutError as error:
            _LOGGER.warning(error)
            raise PyMediaroomError("Timeout connecting to {}".format(self.stb_ip))
        except ConnectionRefusedError as error:
            _LOGGER.warning(error)
            raise PyMediaroomError("Connection refused to {}".format(self.stb_ip))