On boot, slapos script check for Ipv6. If none is found it launch and use OpenVPN

Add possibility to choose  Self hosted image with option --one_disk

The server listen on an unix socket and wait for a json request which
look like :
  {"command": "/command/to/run",
   "timestamp": 0}

The server respond sending back the command it will run.

The server is single threaded on run each command only one by one.

If one command requested two times with the same time stamp, it
will be runned only once.