Change Docker default software dir

Change Docker default software dir

For Docekr 17.xx in Ubuntu 16.04 don't follow the advice of updating the /etc/default/docker and change -g option in DOCKER_OPTS. This advice is for OLD debian using upstar system. If your linux uses Systemd do the following: use the   /etc/docker/daemon.json and add a graph directive

{
    "graph": "/mnt_docker/docker_files"
}