Docker rootless

Personal use:

- just send a message to mailto:lwp@rug.nl stating your intentions
- by default you will be able to run any container but will not be able to mount a local path into the container.
- these limitations can be lifted on a case by case basis (ie. we have to know about it)

Teaching use:

- just send a message to mailto:lwp@rug.nl, we need to know the container name and whether you need to
  forward ports and use local storage. In principle we will mount local storage in /tmp, this way it is cleaned up when the LWP reboots