Support 'headless' applications

Update SpringApplication to run by default in 'headless' mode. This
prevents the AWT system from creating a Java icon (for example in the
OSX dock).

Also update builds to run tests in 'headless' mode.

spring-boot-cli/src/main/java/org/springframework/boot/cli/SpringCli.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2013 the original author or authors.
+ * Copyright 2012-2014 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -90,6 +90,7 @@ public class SpringCli {
 	 * @return a return status code (non boot is used to indicate an error)
 	 */
 	public int runAndHandleErrors(String... args) {
+		System.setProperty("java.awt.headless", Boolean.toString(true));
 		String[] argsWithoutDebugFlags = removeDebugFlags(args);
 		boolean debug = argsWithoutDebugFlags.length != args.length;
 		try {