title: google smart home actions implement offline response issue
body: <p>I implement google smart home actions for plug device,
  I can control on/off plug with no problems, but about implement
  response offline status for Execute and Query, it seems google assistant never get status, it always said "OK, turn on/off plug", My response JSON log from cloud function log as below:</p>
  
  <p>Execute:</p>
  
  <pre><code>   {
      "requestId": "847886417406301663",
      "payload": {
        "commands": {
          "ids": [
            "T90197200015"
          ],
          "status": "ERROR",
          "errorCode": "deviceOffline",
          "online": false
        }
      }
    }
  </code></pre>
  
  <p>Query:</p>
  
  <pre><code>   {
      "requestId": "11887439270473779795",
      "payload": {
        "devices": {
          "T90197200015": {
            "errorCode": "deviceOffline",
            "status": "ERROR",
            "online": false
          }
        }
      }
    }
  </code></pre>
  
  <p>Is the format correct, why google assistant didn't get offline status?</p>
  
  <p>BR,
  Jack</p>