HBASE-24844 RecoverableZookeeper#close followed by ExecutorService shutdown

* Resolves Exception on standalone (master) shutdown

Closes #2239

Signed-off-by: Viraj Jasani <vjasani@apache.org>

hbase-zookeeper/src/main/java/org/apache/hadoop/hbase/zookeeper/ZKWatcher.java

@@ -694,11 +694,12 @@ public class ZKWatcher implements Watcher, Abortable, Closeable {
    */
   @Override
   public void close() {
-    zkEventProcessor.shutdownNow();
     try {
       recoverableZooKeeper.close();
     } catch (InterruptedException e) {
       Thread.currentThread().interrupt();
+    } finally {
+      zkEventProcessor.shutdownNow();
     }
   }