Add TestNG sample application

Add a TestNG sample that also demonstrates @WebIntegrationTest.

See gh-2135

spring-boot-samples/spring-boot-sample-testng/src/main/java/sample/testng/web/SampleController.java

@@ -0,0 +1,38 @@
+/*
+ * Copyright 2012-2015 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 sample.testng.web;
+
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.stereotype.Controller;
+import org.springframework.web.bind.annotation.RequestMapping;
+import org.springframework.web.bind.annotation.ResponseBody;
+
+import sample.testng.service.HelloWorldService;
+
+@Controller
+public class SampleController {
+
+	@Autowired
+	private HelloWorldService helloWorldService;
+
+	@RequestMapping("/")
+	@ResponseBody
+	public String helloWorld() {
+		return this.helloWorldService.getHelloMessage();
+	}
+
+}