void addInputStream(StreamSpec streamSpec, JobNode node) {
    StreamEdge edge = getOrCreateStreamEdge(streamSpec);
    edge.addTargetNode(node);
    node.addInEdge(edge);
    inputStreams.add(edge);
  }
Add a source stream to a {@link JobNode}
@param streamSpec input stream
@param node the job node that consumes from the streamSpec
samza-core/src/main/java/org/apache/samza/execution/JobGraph.java