Minor comments

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

@@ -59,11 +59,11 @@ private[spark] class SparkSubmitArguments(args: Seq[String], env: Map[String, St
   val sparkProperties: HashMap[String, String] = new HashMap[String, String]()
 
   // Standalone cluster mode only
-  var useRest: Boolean = true
   var supervise: Boolean = false
   var driverCores: String = null
   var submissionToKill: String = null
   var submissionToRequestStatusFor: String = null
+  var useRest: Boolean = true // used internally
 
   /** Default properties present in the currently defined defaults file. */
   lazy val defaultSparkProperties: HashMap[String, String] = {

core/src/main/scala/org/apache/spark/deploy/rest/StandaloneRestServer.scala

@@ -439,7 +439,7 @@ private class ErrorServlet extends StandaloneRestServlet {
     // If there is a version mismatch, include the highest protocol version that
     // this server supports in case the client wants to retry with our version
     if (versionMismatch) {
-      error.protocolVersion = serverVersion
+      error.highestProtocolVersion = serverVersion
       response.setStatus(StandaloneRestServer.SC_UNKNOWN_PROTOCOL_VERSION)
     } else {
       response.setStatus(HttpServletResponse.SC_BAD_REQUEST)

core/src/main/scala/org/apache/spark/deploy/rest/SubmitRestProtocolResponse.scala

@@ -76,7 +76,7 @@ private[spark] class SubmissionStatusResponse extends SubmitRestProtocolResponse
 private[spark] class ErrorResponse extends SubmitRestProtocolResponse {
   // The highest protocol version that the server knows about
   // This is set when the client specifies an unknown version
-  var protocolVersion: String = null
+  var highestProtocolVersion: String = null
   protected override def doValidate(): Unit = {
     super.doValidate()
     assertFieldIsSet(message, "message")