Don't add a class option to menu entries generated for ppc64le
    
    For ppc64le a grub config file with menuentry commands is still generated
    even when BLS support is enabled. That's because BLS support was added to
    Petitboot 1.8.0 and any previous version won't be able to parse BLS files.
    
    To make the BLS snippets the source of truth, these are used to generate
    the menuentry commands in the grub config file.
    
    And to keep it consistent across all ppc64le machines regardless of the
    firmware used, the grub config file is also generated for machines with
    OF that use grub2 and would have BLS support.
    
    The BLS snippets created by the kernel package have fields that are used
    to specify the generated menuentry command users and class options. These
    fields are not present in BLS snippets created by OSTree though, so the
    script generating the menuentry commands will add options with an empty
    argument which will lead to grub failing to parse them.
    
    We could check if the field is defined before attempting to add those, but
    since the grub2 blscfg module also supports setting these to variables, it
    could lead to an empty argument even if was defined in the BLS snippet if
    the variable doesn't exist.
    
    So to make more robust, just don't add a class to the menuentry commands
    generated by the script. It's better to not have a class for the menuentry
    than grub2 failing to parse the command and not populating the boot menu.
    
    Resolves: rhbz#1758225
    
    Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>