[SPARK-13769][CORE] Update Java Doc in Spark Submit

JIRA : https://issues.apache.org/jira/browse/SPARK-13769

The java doc here (https://github.com/apache/spark/blob/e97fc7f176f8bf501c9b3afd8410014e3b0e1602/core/src/main/scala/org/apache/spark/deploy/SparkSubmit.scala#L51)
needs to be updated from "The latter two operations are currently supported only for standalone cluster mode." to "The latter two operations are currently supported only for standalone and mesos cluster modes."

Author: Ahmed Kamal <ahmed.kamal@badrit.com>

Closes #11600 from AhmedKamal/SPARK-13769.

core/src/main/scala/org/apache/spark/deploy/SparkSubmit.scala

@@ -48,7 +48,7 @@ import org.apache.spark.util.{ChildFirstURLClassLoader, MutableURLClassLoader, U
 
 /**
  * Whether to submit, kill, or request the status of an application.
- * The latter two operations are currently supported only for standalone cluster mode.
+ * The latter two operations are currently supported only for standalone and Mesos cluster modes.
  */
 private[deploy] object SparkSubmitAction extends Enumeration {
   type SparkSubmitAction = Value