Update the copyright date and make GcpLaunchStage a utility class

Author: rybosome

google-cloud-core/src/main/java/com/google/cloud/GcpLaunchStage.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2016 Google Inc. All Rights Reserved.
+ * Copyright 2017 Google Inc. All Rights Reserved.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -66,4 +66,8 @@ public class GcpLaunchStage {
    */
   @Retention(RetentionPolicy.SOURCE)
   public @interface Deprecated {}
+
+  private GcpLaunchStage() {
+    // Intentionally left blank.
+  }
 }