pungi-koji: new cmd option '--latest-link-status'
    
    Add a new option 'latest-link-status' to pungi-koji, if this is
    specified, pungi will only create the latest symbol link to the compose
    when compose's status matches the specified statuses. The status name is
    case insensitive. If the option is not specified it will act as before.
    
    Example:
    
    pungi-koji --target-dir=_composes --config=data/dummy-pungi.conf \
    --test --latest-link-status=finished --latest-link-status=finished_incomplete
    
    Signed-off-by: Qixiang Wan <qwan@redhat.com>