docker image from usb

Store and load a docker image from USB storage.

# docker save -o /mnt/docker/inapp-v0.1-armhf.tar inapp
# ls -l /mnt/docker/inapp-v0.1-armhf.tar
-rwxr-xr-x 1 root root 212420096 Mar 28 19:27 /mnt/docker/inapp-v0.1-armhf.tar
# docker load -i /mnt/docker/inapp-v0.1-armhf.tar
Loaded image: inapp:latest
# cat /mnt/docker/inapp-v0.1-armhf.tar | xz -z9 > /mnt/docker/inapp-v0.1-armhf.tar.xz
ls -l /mnt/docker/inapp-v0.1-armhf.tar.xz
-rw-r--r-- 1 vjp vjp  49787000 Mar 28 21:43 /mnt/docker/inapp-v0.1-armhf.tar.xz