initramfs-tools will use shellcheck on its own code and will probably
ship a shellcheck autopkgtest that checks its hooks and script
directory. That's how the shellcheck issues in systemd's initramfs-tools
scripts were found.
```
shellcheck -e SC1091 $(find debian/extra/initramfs-tools/ -type f)
```
initramfs-tools is not actually using util-linux mount (yet), so making
mount -n --move the first alternative would trigger an error message if
users have built their initramfs without busybox support.
Due to recent changes in busybox and initramfs-tools the mount
utility is no longer the one from busybox but from util-linux.
The latter does not support mount -o move.
The former supports both -o move and --move, so use it instead to be
compatible with both.
See this discussion for more details:
https://bugs.debian.org/823856Closes: #844775
