Another set of mostly grubby-bls fixes
    
    - grubby-bls: also print the absolute path in the --default-kernel option
      Resolves: rhbz#1649778
    - grubby-bls: allow to specify the same kernel param multiple times
      Resolves: rhbz#1652486
    - grubby-bls: expand kernel options if these are environment variables
      Resolves: rhbz#1649785
    - grubby-bls: always generate the BLS snippets when adding new entries
      Resolves: rhbz#1653365
    - Improve man page for --info option (jstodola)
      Resolves: rhbz#1651672
    - Make the old grubby take precedence over grubby-bls if is installed
      Related: rhbz#165484
    
    Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>