rpm: Abolish image suffix (bsc#1189841).
    
    This is used only with vanilla kernel which is not supported in any way.
    
    The only effect is has is that the image and initrd symlinks are created
    with this suffix.
    
    These symlinks are not used except on s390 where the unsuffixed symlinks
    are used by zipl.
    
    There is no reason why a vanilla kernel could not be used with zipl as
    well as it's quite unexpected to not be able to boot when only a vanilla
    kernel is installed.
    
    Finally we now have a backup zipl kernel so if the vanilla kernel is
    indeed unsuitable the backup kernel can be used.
    
    Signed-off-by: Michal Suchanek <msuchanek@suse.de>