[SPARK-11555] spark on yarn spark-class --num-workers doesn't work

I tested the various options with both spark-submit and spark-class of specifying number of executors in both client and cluster mode where it applied.

--num-workers, --num-executors, spark.executor.instances, SPARK_EXECUTOR_INSTANCES, default nothing supplied

Author: Thomas Graves <tgraves@staydecay.corp.gq1.yahoo.com>

Closes #9523 from tgravescs/SPARK-11555.

yarn/src/main/scala/org/apache/spark/deploy/yarn/ClientArguments.scala

@@ -81,7 +81,7 @@ private[spark] class ClientArguments(args: Array[String], sparkConf: SparkConf)
       .orNull
     // If dynamic allocation is enabled, start at the configured initial number of executors.
     // Default to minExecutors if no initialExecutors is set.
-    numExecutors = YarnSparkHadoopUtil.getInitialTargetExecutorNumber(sparkConf)
+    numExecutors = YarnSparkHadoopUtil.getInitialTargetExecutorNumber(sparkConf, numExecutors)
     principal = Option(principal)
       .orElse(sparkConf.getOption("spark.yarn.principal"))
       .orNull

yarn/src/main/scala/org/apache/spark/deploy/yarn/YarnSparkHadoopUtil.scala

@@ -392,8 +392,11 @@ object YarnSparkHadoopUtil {
   /**
    * Getting the initial target number of executors depends on whether dynamic allocation is
    * enabled.
+   * If not using dynamic allocation it gets the number of executors reqeusted by the user.
    */
-  def getInitialTargetExecutorNumber(conf: SparkConf): Int = {
+  def getInitialTargetExecutorNumber(
+      conf: SparkConf,
+      numExecutors: Int = DEFAULT_NUMBER_EXECUTORS): Int = {
     if (Utils.isDynamicAllocationEnabled(conf)) {
       val minNumExecutors = conf.getInt("spark.dynamicAllocation.minExecutors", 0)
       val initialNumExecutors =
@@ -406,7 +409,7 @@ object YarnSparkHadoopUtil {
       initialNumExecutors
     } else {
       val targetNumExecutors =
-        sys.env.get("SPARK_EXECUTOR_INSTANCES").map(_.toInt).getOrElse(DEFAULT_NUMBER_EXECUTORS)
+        sys.env.get("SPARK_EXECUTOR_INSTANCES").map(_.toInt).getOrElse(numExecutors)
       // System property can override environment variable.
       conf.getInt("spark.executor.instances", targetNumExecutors)
     }