Revert "[SPARK-12345][MESOS] Filter SPARK_HOME when submitting Spark jobs with Mesos cluster mode."

This reverts commit ad8c1f0b84.

core/src/main/scala/org/apache/spark/deploy/rest/mesos/MesosRestServer.scala

@@ -94,12 +94,7 @@ private[mesos] class MesosSubmitRequestServlet(
     val driverMemory = sparkProperties.get("spark.driver.memory")
     val driverCores = sparkProperties.get("spark.driver.cores")
     val appArgs = request.appArgs
-    // We don't want to pass down SPARK_HOME when launching Spark apps
-    // with Mesos cluster mode since it's populated by default on the client and it will
-    // cause spark-submit script to look for files in SPARK_HOME instead.
-    // We only need the ability to specify where to find spark-submit script
-    // which user can user spark.executor.home or spark.home configurations.
-    val environmentVariables = request.environmentVariables.filter(!_.equals("SPARK_HOME"))
+    val environmentVariables = request.environmentVariables
     val name = request.sparkProperties.get("spark.app.name").getOrElse(mainClass)
 
     // Construct driver description

core/src/main/scala/org/apache/spark/scheduler/cluster/mesos/MesosSchedulerUtils.scala

@@ -34,7 +34,7 @@ import org.apache.spark.util.Utils
 
 /**
  * Shared trait for implementing a Mesos Scheduler. This holds common state and helper
- * methods the Mesos scheduler will use.
+ * methods and Mesos scheduler will use.
  */
 private[mesos] trait MesosSchedulerUtils extends Logging {
   // Lock used to wait for scheduler to be registered