The default overcloud-full image uses grub config path
/boot/grub2/grub.cfg however images with EFI boot partitions use grub
config path /boot/efi/EFI/redhat/grub.cfg.
This means for EFI based images, persisting kernel boot args is
currently broken. This change fixes this by checking a known list of
grub.cfg paths and regenerating the config for each file which already
(cherry picked from commit 493cbe8a85)