title: hudson cli to wait for unfinished builds
body: <p>Part of our CI/continuous-test system needs to re-deploy build/test nodes. 
  so far I'm marking them offline and then waiting for twice as long as a build usually takes...<br>
  which is not very elegant. </p>
  
  <p>How can I (after marking it offline) wait for a node to finish its current job(s)?</p>