For each partition, find out if its the root or boot partition and
gather only the relevant information. Make sure that we don't get
information from /boot twice.
Rough draft of image-info, a tool that extracts high-level information
about an os image. It prints this information in JSON form on stdout.
Run it like this:
$ tools/image-info <image>
It supports all images that qemu-ndb supports.
