MAPREDUCE-3801: org.apache.hadoop.mapreduce.v2.app.TestRuntimeEstimators.testExponentialEstimator fails intermittently. Contributed by Jason Lowe

(cherry picked from commit 2cf8927683d49f4cdc3cba038480128c473c5461)

hadoop-mapreduce-project/hadoop-mapreduce-client/hadoop-mapreduce-client-app/src/main/java/org/apache/hadoop/mapreduce/v2/app/speculate/DefaultSpeculator.java

@@ -98,8 +98,6 @@ public class DefaultSpeculator extends AbstractService implements
   private AppContext context;
   private Thread speculationBackgroundThread = null;
   private volatile boolean stopped = false;
-  private BlockingQueue<SpeculatorEvent> eventQueue
-      = new LinkedBlockingQueue<SpeculatorEvent>();
   private TaskRuntimeEstimator estimator;
 
   private BlockingQueue<Object> scanControl = new LinkedBlockingQueue<Object>();
@@ -245,7 +243,7 @@ public class DefaultSpeculator extends AbstractService implements
   // This section is not part of the Speculator interface; it's used only for
   //  testing
   public boolean eventQueueEmpty() {
-    return eventQueue.isEmpty();
+    return scanControl.isEmpty();
   }
 
   // This interface is intended to be used only for test cases.