Extract VM images

[pombredanne]

We should be able to extract VMDK, VDI and similar qcow images, as well as ext2, ext3 and ext4 (and ideally some squashfs too?)

[pombredanne]

Note that one immediate application would be in scancode.io rootfs pipeline

[pombredanne]

I played with a few tools and there is one that shines brightly by @rwmjones and that's https://libguestfs.org/
It works beautifully using the tar-out format.

[tdruez]

The --all-formats is required for the new extraction features but not documented.

More importantly, the all_formats=False was added as an argument of the extract_file function but is not used, see https://github.com/nexB/extractcode/blob/main/src/extractcode/extract.py#L230

Also, why would we want such option in the first place?