grubby-bls: use title field instead of version for zipl default entry
    
    Most bootloaders use the BootLoaderSpec "title" field to name the entries
    in their boot menu. The zipl bootloader used the "version" field instead,
    since it was wrongly assumed that the zipl boot menu didn't support names
    that contained spaces, which are usually present in a BLS "title" field.
    
    But this is not the case, names with space characters are supported by the
    IPL and is just a constraint of the section heading in the zipl.conf file.
    
    To be consistent with all the other bootloaders, zipl now uses the "title"
    field to populate the boot menu entries from BLS files. So change grubby
    to use the "title" field to set the default entry of the "version" field.
    
    Related: rhbz#1645200
    
    Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>