support stream output for yakkety builds
For yakkety builds:
- yakkety build output renames the -disk1.img file to .img
but stream data should maintain -disk1.img as the ftype and item key.
- -root.tar.gz and -root.tar.xz files are not produced
- squashfs images are available (and also were available partially through
xenial)
As a cleanup, we a helper to ubuntu_versions to compare versions more
directly. String compare was less useful in some cases and also would end
up breaking after 'z' because whatever release comes after z would string
sort to < z.
This also adds a simple tool for comparing two trees output of 'make exdata'.
./tools/compare-test-data ../trunk.dist ./
will output a 'diff' from old to new list of files indexed.