unduplicate / refactor umount_kill.sh

[adrelanos]

There are 3 different versions in 3 different repositories.

• https://github.com/marmarek/qubes-builder-debian/blob/master/scripts/umount_kill.sh
• https://github.com/marmarek/qubes-linux-template-builder/blob/master/umount_kill.sh
• https://github.com/marmarek/qubes-builder/blob/master/scripts/umount_kill.sh

Step one, sync them. That alone would be worthwhile. The following two have only a single lined diff.

diff ./qubes-builder-debian/scripts/umount_kill.sh ./qubes-builder/scripts/umount_kill.sh

Step two, is it possible to have only one of these files in the Qubes source?

I was also always wondering if such a script and other image mount/umount/chroot related code could be upstreamed somewhere instead of reinventing it in every project. libguestfs (slow) does not want kpartx based mount scripts.

@nrgaway