Upgrade to Servlet 3.1, Tomcat 8 and Jetty 9

Upgrade to latest versions of Tomcat and Jetty and to the latest Servlet
API whilst will remaining compatible with Tomcat 7 and Jetty 8.

Fixes gh-1832, gh-369

spring-boot-cli/src/test/java/org/springframework/boot/cli/CliTester.java

@@ -20,7 +20,9 @@ import java.io.BufferedReader;
 import java.io.File;
 import java.io.InputStream;
 import java.io.InputStreamReader;
+import java.lang.reflect.Field;
 import java.net.URI;
+import java.net.URL;
 import java.util.ArrayList;
 import java.util.List;
 import java.util.concurrent.Callable;
@@ -94,6 +96,7 @@ public class CliTester implements TestRule {
 
 	private <T extends OptionParsingCommand> Future<T> submitCommand(final T command,
 			String... args) {
+		clearUrlHandler();
 		final String[] sources = getSources(args);
 		return Executors.newSingleThreadExecutor().submit(new Callable<T>() {
 			@Override
@@ -112,6 +115,21 @@ public class CliTester implements TestRule {
 		});
 	}
 
+	/**
+	 * The TomcatURLStreamHandlerFactory fails if the factory is already set, use
+	 * reflection to reset it.
+	 */
+	private void clearUrlHandler() {
+		try {
+			Field field = URL.class.getDeclaredField("factory");
+			field.setAccessible(true);
+			field.set(null, null);
+		}
+		catch (Exception ex) {
+			throw new IllegalStateException(ex);
+		}
+	}
+
 	protected String[] getSources(String... args) {
 		final String[] sources = new String[args.length];
 		for (int i = 0; i < args.length; i++) {