Add some fixes for BLS parsing logic and also make 20-grub.install script
to query the relative path of the kernel and initramfs images, so BLS can
also work when /boot is not a mount point or is a btrfs subvolume.
Also pull some build fixes.
Resolves: rhbz#1588184
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
