title: cloudformation update-stack not idempotent
body: <p>I have a template that creates 2 EC2 instances.</p>
  
  <p>I update the template and remove one of the instances from it</p>
  
  <p>Then i run update stack- cloud formation will not remove that ec2 instance right? </p>
  
  <p>This is why I use terraform. Is there a way to make cloudformation behave this way?</p>