Fix ./test script to stop container faster and more reliably

[vorburger]

@edewit this is also in #429 but technically unrelated to that, it just bugged me enough that I fixed it there.

Do you want to review and merge this here already, before you get to fixing #429 itself?

[vorburger]

Note this is technically 2 separate changes:

1. it appears the rm --force is more reliable than the stop (and I give it less time)
2. stopping the previous Minecraft server container before starting to re-build the new version is probably a better order, for local build performance