Fix checkstyle and license issues

Author: anmolnar

dev/docker/Dockerfile

@@ -17,7 +17,7 @@
 # under the License.
 #
 
-FROM maven:3.8.4-jdk-8
+FROM maven:3.8.4-jdk-11
 
 RUN apt-get update
 RUN apt-get install -y \

zookeeper-server/src/main/java/org/apache/zookeeper/common/ZKConfig.java

@@ -29,7 +29,6 @@
 import java.util.Map;
 import java.util.Map.Entry;
 import java.util.Properties;
-
 import org.apache.zookeeper.Environment;
 import org.apache.zookeeper.server.util.VerifyingFileFactory;
 import org.slf4j.Logger;

zookeeper-server/src/test/java/org/apache/zookeeper/common/ZKConfigTest.java

@@ -22,17 +22,15 @@
 import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertNotNull;
 import static org.junit.jupiter.api.Assertions.assertTrue;
-
+import ch.qos.logback.classic.Level;
+import java.io.File;
+import java.io.IOException;
 import org.apache.zookeeper.test.LoggerTestTool;
 import org.junit.jupiter.api.AfterAll;
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.BeforeAll;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.Timeout;
-import ch.qos.logback.classic.Level;
-
-import java.io.File;
-import java.io.IOException;
 
 public class ZKConfigTest {
 

zookeeper-server/src/test/java/org/apache/zookeeper/test/LoggerTestTool.java

@@ -30,7 +30,6 @@
 import java.io.IOException;
 import java.io.LineNumberReader;
 import java.io.StringReader;
-
 import org.slf4j.LoggerFactory;
 
 public class LoggerTestTool implements AutoCloseable {

zookeeper-server/src/test/resources/zookeeper-client.config

@@ -1,5 +1,19 @@
+# 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.
+
 # Sample secrets
 zookeeper.ssl.keyStore.password=FileSecret456!
 zookeeper.ssl.keyStore.passwordPath=/home/zookeeper/top_secret.txt
 ssl.quorum.keyStore.password=AnotherFileSecret789!
-