HDDS-744. Fix ASF license warning in PipelineNotFoundException class.

Contributed by Lokesh Jain.

hadoop-hdds/common/src/main/java/org/apache/hadoop/hdds/scm/pipeline/PipelineNotFoundException.java

@@ -1,3 +1,21 @@
+/*
+ * 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.
+ */
+
 package org.apache.hadoop.hdds.scm.pipeline;
 
 import java.io.IOException;