Remove sleep when waiting for node closure (#1722)

Signed-off-by: Peter Nied <petern@amazon.com>

src/test/java/org/opensearch/security/test/helper/cluster/ClusterHelper.java

@@ -39,6 +39,7 @@
 import java.util.SortedSet;
 import java.util.TreeSet;
 import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicReference;
 import java.util.stream.Collectors;
 
@@ -247,18 +248,18 @@ public final void stopCluster() throws Exception {
 
     private void closeAllNodes() throws  Exception {
         //close non master nodes
-        opensearchNodes.stream().filter(n->!n.isMasterEligible()).forEach(node->closeNode(node));
+        opensearchNodes.stream().filter(n->!n.isMasterEligible()).forEach(ClusterHelper::closeNode);
 
         //close master nodes
-        opensearchNodes.stream().filter(n->n.isMasterEligible()).forEach(node->closeNode(node));
+        opensearchNodes.stream().filter(n->n.isMasterEligible()).forEach(ClusterHelper::closeNode);
         opensearchNodes.clear();
         clusterState = ClusterState.STOPPED;
     }
 
     private static void closeNode(Node node) {
         try {
             node.close();
-            Thread.sleep(250);
+            node.awaitClose(250, TimeUnit.MILLISECONDS);
         } catch (Throwable e) {
             //ignore
         }