Two more BLS fixes
    
    Only set blsdir if /boot/loader/entries is in a btrfs or zfs partition
      Related: rhbz#1688453
    Fix some BLS snippets not being displayed in the GRUB menu
      Resolves: rhbz#1691232
    
    Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>