kernel gi: Add resolving of the dracut and grub-mkconfig binary path

[geaaru]

Just to fix these errors:

command: exec: "dracut": executable file not found in $PATH. I go ahead.
No valid links found. I set links to kernel 5.4.231.
Creating grub config file /boot/grub/grub.cfg...
Error on update grub.cfg: Error on start grub-mkconfig command: exec: "grub-mkconfig": executable file not found in $PATH

when $PATH is not set I could follow what I did with env-update: https://github.com/macaroni-os/macaronictl/blob/master/pkg/portage/env-update.go#L176