Add value alias for SpringApplicationConfiguration

Given that Spring Boot uses java config accross the board, a new `value`
attribute is now aliased to the existing `classes` attribute such that
one could write the following:

@SpringApplicationConfiguration(MyConfig.class)
public class MyTest {}

Closes gh-3635

spring-boot-samples/spring-boot-sample-data-gemfire/src/test/java/sample/data/gemfire/SampleDataGemFireApplicationTests.java

@@ -42,7 +42,7 @@ import static org.junit.Assert.assertTrue;
  * @author John Blum
  */
 @RunWith(SpringJUnit4ClassRunner.class)
-@SpringApplicationConfiguration(classes = SampleDataGemFireApplication.class)
+@SpringApplicationConfiguration(SampleDataGemFireApplication.class)
 public class SampleDataGemFireApplicationTests {
 
 	@Autowired