Cleanup shutdown (elastic#96232)

This commit moves the close preparation hook call into the shutdown try.
It also imporoves the error message when an error occurs, and removes an
unnecessary null check that is never possible.

relates elastic#95850

Author: rjernst

server/src/main/java/org/elasticsearch/bootstrap/Elasticsearch.java

@@ -44,6 +44,7 @@
 import java.security.Permission;
 import java.security.Security;
 import java.util.List;
+import java.util.Objects;
 import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.TimeUnit;
 
@@ -423,8 +424,8 @@ private static Environment createEnvironment(Path configDir, Settings initialSet
     private final Thread keepAliveThread;
 
     private Elasticsearch(Spawner spawner, Node node) {
-        this.spawner = spawner;
-        this.node = node;
+        this.spawner = Objects.requireNonNull(spawner);
+        this.node = Objects.requireNonNull(node);
         this.keepAliveThread = new Thread(() -> {
             try {
                 keepAliveLatch.await();
@@ -444,16 +445,16 @@ private static void shutdown() {
             return; // never got far enough
         }
         var es = INSTANCE;
-        es.node.prepareForClose();
         try {
+            es.node.prepareForClose();
             IOUtils.close(es.node, es.spawner);
-            if (es.node != null && es.node.awaitClose(10, TimeUnit.SECONDS) == false) {
+            if (es.node.awaitClose(10, TimeUnit.SECONDS) == false) {
                 throw new IllegalStateException(
                     "Node didn't stop within 10 seconds. " + "Any outstanding requests or tasks might get killed."
                 );
             }
         } catch (IOException ex) {
-            throw new ElasticsearchException("failed to stop node", ex);
+            throw new ElasticsearchException("Failure occurred while shutting down node", ex);
         } catch (InterruptedException e) {
             LogManager.getLogger(Elasticsearch.class).warn("Thread got interrupted while waiting for the node to shutdown.");
             Thread.currentThread().interrupt();