A set of fixes mostly BLS related
    
    Fix --bls-directory option comment in grub2-switch-to-blscfg man page
      Resolves: rhbz#1714835
    10_linux_bls: use '=' to separate --id argument due a Petitboot bug
    grub-set-bootflag: Print an error if failing to read from grubenv
      Resolves: rhbz#1702354
    10_linux: generate BLS section even if no kernels are found in /boot
    10_linux: don't search for OSTree kernels
    
    Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>