Add exclude attribute to @SpringBootApplication

Fixes gh-2207

spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/SpringBootApplication.java

@@ -46,4 +46,9 @@ import org.springframework.context.annotation.Configuration;
 @ComponentScan
 public @interface SpringBootApplication {
 
+	/**
+	 * Exclude specific auto-configuration classes such that they will never be applied.
+	 */
+	Class<?>[] exclude() default {};
+
 }