Fix logic that checks for kernelopts in BLS files and some cleanups
    
    grubby-bls: don't print rpm-sort error messages
      Resolves: rhbz#1731924
    grubby-bls: remove -o option and support -c for ppc64le grub config
      Resolves: rhbz#1758598
    grubby-bls: fix logic to check if the kernelopts var is defined in a BLS
      Resolves: rhbz#1726514
    
    Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>