Add b2c from freedesktop/ci-templates/-/merge_requests/105
This is on top of !59 (merged).
While working on freedesktop/ci-templates!105 (merged), it was more and more clear that the script I was writing would be better if it were tied to boot2container directly.
So here comes the script, in a pruned version which should hopefully be generic enough.
The idea is to be able to quickly run b2c in qemu without having to deal with a lot of parameters.
Having the script here allows to keep changes in the init script and in b2c
in parallel, without having discrepancies in versions.
Marking as a draft because freedesktop/ci-templates!105 (merged) needs to be rewritten.