In working to get the SparkGraphComputer to work with JanusGraph, I came across this project for Titan. 
https://github.com/imri/mizo

I can get it to compile for JanusGraph, but not work with the files in HBase.  Specifically what to set for the hdfs path here:

long count = new MizoBuilder()
                .titanConfigPath("titan-graph.properties")
                .regionDirectoriesPath("hdfs://my-graph/*/e")
                .parseInEdges(v -> false)
                .verticesRDD(sc)
                .toJavaRDD()
                .count();

Has this been used with JanusGraph?

-Joe