Add btrfs snapshot submenu and move grub2-probe to tools-minimal
    
    The btrfs snapshot submenu was removed because it broke the old grubby tool
    since it searched for "menuentry". But now that a BLS config is supported,
    this can be added again as long as grubby isn't used.
    
    This patch also moves the grub2-probe tool to the tools-minimal package to
    prevent a circular dependency since the grub2-tools package depends on the
    os-prober package, but os-prober package needs grub2-probe as a dependency.
    
    So instead of making os-prober to depend on grub2-tools, it can be made to
    depend on the grub2-tools-minimal subpackage.
    
    Resolves: rhbz#1715994
    
    Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>