ZOOKEEPER-3831: [ADDENDUM] fix apache-rat error, add missing apache license

I think we will need to push this to both master and branch-3.6.

Author: Mate Szalay-Beko <symat@apache.org>

Reviewers: Norbert Kalmar <nkalmar@apache.org>

Closes #1376 from symat/rat-fix

zookeeper-compatibility-tests/zookeeper-compatibility-tests-curator/pom.xml

@@ -1,4 +1,23 @@
 <?xml version="1.0" encoding="UTF-8"?>
+<!--
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+-->
 <project xmlns="http://maven.apache.org/POM/4.0.0"
          xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
          xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">