[test] wait until master actually has applied cluster state that contains second node

If we don't wait we might retrieve the cluster state before second node
was added when we try to add the delegate in which the discovery node for
node_2 is null.

core/src/test/java/org/elasticsearch/indices/store/IndicesStoreIntegrationIT.java

@@ -179,6 +179,8 @@ public class IndicesStoreIntegrationIT extends ESIntegTestCase {
         assertThat(Files.exists(indexDirectory(node_1, "test")), equalTo(true));
 
         final String node_2 = internalCluster().startDataOnlyNode(Settings.builder().build());
+        assertFalse(client().admin().cluster().prepareHealth().setWaitForNodes("2").get().isTimedOut());
+
         assertThat(Files.exists(shardDirectory(node_1, "test", 0)), equalTo(true));
         assertThat(Files.exists(indexDirectory(node_1, "test")), equalTo(true));
         assertThat(Files.exists(shardDirectory(node_2, "test", 0)), equalTo(false));