title: How to make AWS Lambda wait for a shadow updated topic
body: <p>My desired flow is:</p>
  
  <ol>
  <li>ask my iot device to do something using AVS sdk</li>
  <li>aws lambda triggered and update the device shadow</li>
  <li><p>iot device triggered based on the shadow topic: delta and do something locally. Publish the status to shadow when done doing something</p></li>
  <li><p>aws lambda sends voice feedback to my iot device to tell users the reported status</p></li>
  </ol>
  
  <p>I am stuck in point 4 since I dont know how to trigger AVS(ASK)'s speech response only after the topic is updated "within the same lambda triggered by AVS (as mentioned in point 1 and 2).</p>