A bisect feature to Launcher

[DamienCassou]

Reported by Ben Coman:

Introduce a feature similar to git-bisect. (Disclaimer, I've never used git-bisect but it seems like a really useful feature to have)

git bisect is a tool that allows you to find an offending commit. Let’s say you’ve come across a bug in your codebase and you’re unsure of when it was introduced. If you can find a commit where the code works properly and a commit where it doesn’t, you don’t have to trace down the offending commit by hand; git-bisect will do that for you.

http://robots.thoughtbot.com/post/57797091118/git-bisect

https://www.kernel.org/pub/software/scm/git/docs/git-bisect.html

Could have two modes:

1. In Manual Mode, the user launches the image in the middle of good & bad images. In the background the next two choices of middle could downloaded ready for an immediate start after the user finishes testing. When the user quits the image under test, it automatically returns to Launcher which asks the question "good/bad?" and automatically launches the next test image.
2. In Automated Mode you could design a Test that distinguishes good/bad behaviour and have that supplied as a startup script for the launched image. Based on the result returned to the Launcher, it can selected the next image to try. The additional benefit is the generation of a good Test that can later be integrated into the image.

I've set the priority to "6 - On Hold" since its a stretch goal, but I can seed the idea since I think it is worth considering as a long term plan.