void addOutputStream(StreamSpec streamSpec, JobNode node) {
    StreamEdge edge = getOrCreateStreamEdge(streamSpec);
    edge.addSourceNode(node);
    node.addOutEdge(edge);
    outputStreams.add(edge);
  }
Add an output stream to a {@link JobNode}
@param streamSpec output stream
@param node the job node that outputs to the output stream
samza-core/src/main/java/org/apache/samza/execution/JobGraph.java