title: Force ansible to fail (return non-zero code) if there are any 'changed' tasks
body: <p>I want to a perform convergence test for a playbook. Convergence test checks if second run of the same playbook make no changes.</p>
  
  <p>Is there a way to say Ansible "make exit code non-zero if there was a task in 'changed' state?". I can parse stdout, but it's ugly.</p>
  
  <p>Example:</p>
  
  <pre><code>set -e
  ansible-playbook -i inventory.yaml site.yaml  # normal run
  ansible-playbook --help-me-here -i inventory.yaml site.yaml  # should return non-zero if anything changed.
  
  </code></pre>