[BUG] GRUB 2.02~beta2-2: /etc/grub.d/00_default looks for grubenv in $prefix

[grub-devel at pengaru.com]

Hello,

After setting GRUB_DEFAULT=saved in /etc/default/grub, `grub-set-default`
appears to still have no effect on boot.

Upon further investigation /boot/grub/grubenv was seen to be properly
updated with the desired default id.  However, the grub.cfg generated by
`grub-mkconfig` (via `update-grub2`) was expecting the environment file to
exist at $prefix/grubenv.  With $prefix set to /usr, this appeared obviously
wrong.

After changing /etc/grub.d/00_header to use $grubdir/grubenv instead, things
appear to be working as expected following another `update-grub2`.

Regards,
Vito Caputo