The call above in effect pulls the source (so we do not have to use a separate pullstream), creates a live flv, and then creates three streams stream100, stream200 and stream300, respectively. The vbr is associated with the stream in the order they are defined.
Then you can push the the streams defined above to rtmp://54.187.191.137/live.
By the way, not passing the videoBitRates as you did below means no video.