Move back to JUnit 4 until SUREFIRE-1614 has been resolved

See gh-14736
See gh-14737
See gh-14738

spring-boot-samples/spring-boot-sample-servlet/src/test/java/sample/servlet/SampleServletApplicationTests.java

@@ -18,7 +18,8 @@ package sample.servlet;
 
 import java.util.Collections;
 
-import org.junit.jupiter.api.Test;
+import org.junit.Test;
+import org.junit.runner.RunWith;
 
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.boot.test.context.SpringBootTest;
@@ -30,6 +31,7 @@ import org.springframework.http.HttpMethod;
 import org.springframework.http.HttpStatus;
 import org.springframework.http.MediaType;
 import org.springframework.http.ResponseEntity;
+import org.springframework.test.context.junit4.SpringRunner;
 
 import static org.assertj.core.api.Assertions.assertThat;
 
@@ -38,7 +40,7 @@ import static org.assertj.core.api.Assertions.assertThat;
  *
  * @author Dave Syer
  */
-
+@RunWith(SpringRunner.class)
 @SpringBootTest(webEnvironment = WebEnvironment.RANDOM_PORT)
 public class SampleServletApplicationTests {