This is related to:
| commit
642e1b389347bcb8d6e44b483c327e45225427f4
| Author: Michael Prokop <mika@grml.org>
| Date: Thu Nov 22 23:54:10 2018 +0100
|
| Ensure GRUB finds the running ISO
By using the same approach for setting $root within GRUB
also for the Secure Boot GRUB configuration we ensure to
apply the same safety measures to Secure Boot mode.