Disk image is too large

[fwilhe]

What happened: When building the images, one gets a huge disk image. Proper gardenlinux optimizes the disk size on build, this has not been done here yet.

What you expected to happen: The disk is not 6gig on disk when building when it could also be 1gig, but still the disk should be able to grow when needed (so enough space for updates is available).

How to reproduce it (as minimally and precisely as possible): Run the build commands from the readme and observe the size of the created raw files.

Anything else we need to know:

Environment: