This patch adds the wsl-tarball image type. The difference between
this and the plain tarball type is the creation of the symlinks at
/bin/sh and /bin/mount.

These are necessary for the first boot to work after importing. We
can’t rely on special-files-service-type for this because the system
is not activated yet, and the /bin/sh symlink initiates the first
system activation.

Thanks,
–
Alex Griffin