Actually restore lost Node#start no-op check

This commit really reverts the inadvertent removal of allowing duplicate
calls to Node#start to be a no-op (but was mistakenly restored to
Node#stop in ddfa3a661510f25c2ce431dfd6fb86ac11eb8888).

core/src/main/java/org/elasticsearch/node/Node.java

@@ -266,6 +266,10 @@ public class Node implements Closeable {
      * Start the node. If the node is already started, this method is no-op.
      */
     public Node start() {
+        if (!lifecycle.moveToStarted()) {
+            return this;
+        }
+
         ESLogger logger = Loggers.getLogger(Node.class, NODE_NAME_SETTING.get(settings));
         logger.info("starting ...");
         // hack around dependency injection problem (for now...)