title: Will actionlib.SimpleActionClient.cancel_all_goals block until completion?
body: <p>Suppose I have the following:</p>
  
  <pre class="lang-python prettyprint-override"><code>action_client.cancel_all_goals()
  print(action_client.get_status() != 'ACTIVE')
  </code></pre>
  
  <p>Is the above guaranteed to print <code>True</code> every time?</p>
  
  <p>In other words, does <code>SimpleActionClient.cancel_all_goals()</code> cancel all goals before returning, or does it just send instructions to
  cancel goals without waiting for the goals to be really cancelled?</p>