Another set of BLS fixes
    
    BLS files should only be copied by grub-switch-to-blscfg if BLS isn't set
      Related: rhbz#1638117
    Fix get_entry_number() wrongly dereferencing the tail pointer
      Resolves: rhbz#1654936
    Make grub2-mkconfig to honour GRUB_CMDLINE_LINUX in /etc/default/grub
      Resolves: rhbz#1637875
    
    Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>