1. 调用父类（设备相关）_on_connect函数，订阅相关主题，因为网关在thingsboard中也是一个设备

      1. # 网关设备调用服务端，服务端响应
      2. RPC_RESPONSE_TOPIC = 'v1/devices/me/rpc/response/'
      3. # 服务器端rpc调用网关设备
      4. RPC_REQUEST_TOPIC = 'v1/devices/me/rpc/request/'
      5. # 网关设备属性发生变化会通知该主题
      6. ATTRIBUTES_TOPIC = 'v1/devices/me/attributes'
      7. # 获取网关设备属性需要订阅该主题
      8. ATTRIBUTES_TOPIC = 'v1/devices/me/attributes/response/+'

    2. 网关客户端订阅：

      1. GATEWAY_ATTRIBUTES_TOPIC = "v1/gateway/attributes"
      2. GATEWAY_ATTRIBUTES_RESPONSE_TOPIC = "v1/gateway/attributes/response"
      3. GATEWAY_RPC_TOPIC = "v1/gateway/rpc"

      一共订阅了7个主题