Stabilize testDropCurrentStateRunningTask (#1478)

This commit stabilizes the TestDropCurrentStateRunningTask.
diff --git a/helix-core/src/test/java/org/apache/helix/integration/task/TestDropCurrentStateRunningTask.java b/helix-core/src/test/java/org/apache/helix/integration/task/TestDropCurrentStateRunningTask.java
index f3e3dcf..c932634 100644
--- a/helix-core/src/test/java/org/apache/helix/integration/task/TestDropCurrentStateRunningTask.java
+++ b/helix-core/src/test/java/org/apache/helix/integration/task/TestDropCurrentStateRunningTask.java
@@ -149,7 +149,7 @@
                             .get(currentStatePathP1, new Stat(), AccessOption.PERSISTENT) == null),
                     TestHelper.WAIT_DURATION));
 
-    _driver.waitToStop(workflowName, TestHelper.WAIT_DURATION);
+    _driver.stop(workflowName);
   }
 
   @Test(dependsOnMethods = "testDropCurrentStateRunningTask")