Consider WebAppConfiguration in @SpringBootTest

Update SpringBootTestContextBootstrapper to consider the
`@WebAppConfiguration` annotation and use sensible resourceBasePath
defaults.

Fixes gh-6371

spring-boot-samples/spring-boot-sample-war/src/test/java/sample/war/WarApplicationResourceTests.java

@@ -0,0 +1,42 @@
+/*
+ * Copyright 2012-2016 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.war;
+
+import org.junit.Test;
+import org.junit.runner.RunWith;
+
+import org.springframework.beans.factory.annotation.Value;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.test.context.junit4.SpringRunner;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+@RunWith(SpringRunner.class)
+@SpringBootTest
+public class WarApplicationResourceTests {
+
+	// gh-6371
+
+	@Value("${demo.string.value}")
+	private String demoStringValue;
+
+	@Test
+	public void contextLoads() {
+		assertThat(this.demoStringValue).isEqualTo("demo");
+	}
+
+}