[Storage] Bucket lock (#3574)

Author: frankyn

java-storage-nio/google-cloud-nio/src/main/java/com/google/cloud/storage/contrib/nio/testing/FakeStorageRpc.java

@@ -65,6 +65,7 @@
  *   <li>createBatch
  *   <li>checksums, etags
  *   <li>IAM operations</li>
+ *   <li>BucketLock operations</li>
  *   </ul>
  * </ul>
  */
@@ -520,6 +521,11 @@ public Notification createNotification(String bucket, Notification notification)
     throw new UnsupportedOperationException();
   }
 
+  @Override
+  public Bucket lockRetentionPolicy(Bucket bucket, Map<Option, ?> options) {
+    throw new UnsupportedOperationException();
+  }
+
   @Override
   public ServiceAccount getServiceAccount(String projectId) {
     return null;