Use full EFI path to map drives for grub (#598572)
    
    NOTE: This requires grub-0.97-66 to work correctly.
    
    On EFI we map the boot drive so that there is no question as to where
    /boot is located. This requires a change in grub to parse the EFI
    device path from the map command.
    
    Also make all efibootmgr invocations use PATH instead of hardcoded
    locations.
    
    Related: rhbz#598572