title: Safe delete docker tmp folder
body: <p>I had to cancel a docker build 2 times during "uploading context" phase.
  I figure out what I was doing wrong, but know I have some huge files in docker tmp folder. </p>
  
  <p>Can I safely delete these folders? What about deleting the whole "/var/lib/docker/tmp" folder?</p>
  
  <ul>
  <li>/var/lib/docker/tmp/docker-builder185153115/</li>
  <li>/var/lib/docker/tmp/docker-builder737796513/</li>
  </ul>