F25: Fix %posttrans to properly write /usr/lib/variant
    
    We were calling convert_to_edition() instead of install_edition(),
    which doesn't write the /usr/lib/variant file.
    
    install_edition() also checks for pre-existence of the variant
    file, so we don't need to do that additionally.
    
    Signed-off-by: Stephen Gallagher <sgallagh@redhat.com>