* Make 'grub-mkconfig' command name configurable
- Use 'grub-mkconfig' as the default
- Note that some systems use 'grub2-mkconfig'
- Update 10-update_grub.conf to use the configurable grub directory name
- Refactor the systemd commands for clarity and to avoid duplicate regeneration on first run
* Update check_uuid_required() to work for partial regeneration of the GRUB menu