Revert "webflux-form sample uses Tomcat"

This reverts commit 67bb91bb76.

We can use Netty again now that reactor/reactor-netty#248 has
been resolved.

Fixes: gh-4923

samples/javaconfig/webflux-form/src/integration-test/java/sample/WebfluxFormApplicationTests.java

@@ -28,20 +28,17 @@ import org.springframework.test.context.junit4.SpringRunner;
 import sample.webdriver.IndexPage;
 import sample.webdriver.LoginPage;
 
-import java.io.IOException;
-import java.net.ServerSocket;
-
 /**
  * @author Rob Winch
  * @since 5.0
  */
 @RunWith(SpringRunner.class)
 @ContextConfiguration(classes = WebfluxFormApplication.class)
-@TestPropertySource(properties = "server.port=#{T(sample.WebfluxFormApplicationTests).availablePort()}")
+@TestPropertySource(properties = "server.port=0")
 public class WebfluxFormApplicationTests {
 	WebDriver driver;
 
-	@Value("#{@tomcat.server.port}")
+	@Value("#{@nettyContext.address().getPort()}")
 	int port;
 
 	@Before
@@ -79,12 +76,4 @@ public class WebfluxFormApplicationTests {
 			.assertAt()
 			.assertLogout();
 	}
-
-	public static final int availablePort() {
-		try(ServerSocket socket = new ServerSocket(0)) {
-			return socket.getLocalPort();
-		} catch(IOException e) {
-			throw new RuntimeException(e);
-		}
-	}
 }