Mount DSVM data disk by default and route Docker images to it
A Linux DSVM currently comes with a small OS disk that is nearly full to begin with, and if the user forgets that Docker images are stored on it, they quickly fill the disk, at which point they have a huge headache to deal with. Also, the 1.5Tb data disk is oddly not mounted at first, which makes it invisible. Why not mount the data disk automatically and make Docker save new images on the data disk (see [here](https://www.guguweb.com/2019/02/07/how-to-move-docker-data-directory-to-another-location-on-ubuntu/))?
