Added TaskExecutionListenerSupport

This commit adds the TaskExecutionListenerSupport, a no-op
implementation of the TaskExecutionListner. This allows a user to extend
the TaskExecutionListenerSupport and simply override what they need
instead of implementing all of the methods.

spring-cloud-task-core/src/main/java/org/springframework/cloud/task/listener/TaskExecutionListenerSupport.java

@@ -0,0 +1,42 @@
+/*
+ * Copyright 2017 the original author or authors.
+ *
+ * Licensed 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.springframework.cloud.task.listener;
+
+import org.springframework.cloud.task.repository.TaskExecution;
+
+/**
+ * A no-op implementation of the {@link TaskExecutionListener} to allow for overriding
+ * only the methods of interest.
+ *
+ * @author Michael Minella
+ * @since 1.2
+ */
+public class TaskExecutionListenerSupport implements TaskExecutionListener {
+	@Override
+	public void onTaskStartup(TaskExecution taskExecution) {
+
+	}
+
+	@Override
+	public void onTaskEnd(TaskExecution taskExecution) {
+
+	}
+
+	@Override
+	public void onTaskFailed(TaskExecution taskExecution, Throwable throwable) {
+
+	}
+}