title: Subprocess timeout failure
body: <p>I want to use a timeout on a subprocess</p>
  
  <pre><code> from subprocess32 import check_output
   output = check_output("sleep 30", shell=True, timeout=1)
  </code></pre>
  
  <p>Unfortunately, whilst this raises a timeout error, it does so after 30 seconds. It seems that check_output cannot interrupt the shell command.</p>
  
  <p>What can I do on on the Python side to stop this? 
  I suspect that subprocess32 fails to kill the timed out process.</p>