title: Missing SPARK_HOME when using SparkLauncher on AWS EMR cluster
body: <p>I am using EMR 5.0 with Spark 2.0.0. 
  I am trying to run child spark application from Scala spark application using org.apache.spark.launcher.SparkLauncher</p>
  
  <p>I need to set SPARK_HOME using setSparkHome: </p>
  
  <pre><code> var handle = new SparkLauncher()
      .setAppResource("s3://my-bucket/python_code.py")
      .setAppName("PythonAPP")
      .setMaster("spark://" + sparkSession.conf.get("spark.driver.host") +":"+ sparkSession.conf.get("spark.driver.port"))
      .setVerbose(true)
      .setConf(SparkLauncher.EXECUTOR_CORES, "1")
      .setSparkHome("/srv/spark") // not working
      .setDeployMode("client")
      .startApplication(
        new SparkAppHandle.Listener() {
  
          override def infoChanged(hndl: SparkAppHandle): Unit = {
            System.out.println(hndl.getState() + " new  state !")
          }
  
          override def stateChanged(hndl: SparkAppHandle): Unit = {
            System.out.println(hndl.getState() + "    new  state !")
          }
        })
  </code></pre>
  
  <p>Where can I find the appropriate path to my Spark Home ? 
  The cluster is built from 1 Master, 1 Core and 1 Task servers. </p>
  
  <p>Thanks! </p>