[scripts] move GRUB2 Live directory from /boot/grub to /boot/sabayon

This is not /boot/grub for a very good reason:
 Our Live media uses /boot/sabayon instead of /boot/grub
 and this has also the side effect that we can put
 /boot/sabayon into the EFI Boot Partition avoiding
 name clashing. Our /boot/sabayon inside that partition
 will contain a simple grub.cfg doing two things:

 1. set the correct prefix to the real grub boot partition
    (via set prefix=(hdX,X)/boot/grub
 2. load the real grub.cfg file (via configfile (hdX,X)/...)

 In this way, we can ship a SecureBoot signed grubx64.efi
 file and have it working with all the partition layouts.
 The "bootstrap" grub.cfg file is created by our scripts
 that are sourced by grub-mkconfig.

scripts/spinbase_pre_iso_script.sh

@@ -42,7 +42,7 @@ ver=${RELEASE_VERSION}
 
 isolinux_dest="${CDROOT_DIR}/isolinux/txt.cfg"
 isolinux_dest_txt="${CDROOT_DIR}/isolinux/isolinux.txt"
-grub_dest="${CDROOT_DIR}/boot/grub/grub.cfg"
+grub_dest="${CDROOT_DIR}/boot/sabayon/grub.cfg"
 
 for path in "${isolinux_dest}" "${isolinux_dest_txt}" "${grub_dest}"; do
 	sed -i "s/__VERSION__/${ver}/g" "${path}" || exit 1