build: hard exit on success to avoid hanging

build: hard exit on success to avoid hanging

Something is preventing `fdroid build --all` from exiting after a long
run.  @bubu, @uniqx and I think it is because of the use of
AsynchronousFileReader, somehow it's thread does not exit. So the
workaround for now is to just try a hard exit instead of waiting for
things to finish cleanly with `sys.exit(0)`.

https://jenkins.debian.net/job/reproducible_fdroid_build_apps/94/console