Some fixes and improvements

  * Put full path in the crontab (else it can't find the script)
  * Setup the crontab with `crontab <<EOF` (strangely, `crontab -u root <<EOF` does not work)
  * Move the output directory (containing the important packages!!) to /repository/debian and expose it as a volume
  * Remove sudo access from 'user' (as it's not necessary; nsenter can get into the container for debugging).