refs #966 - read optional 'name' property from failure

Allow to pass in a custom name to `casper.test.fail()` which is used in the junit xml report.

```
this.test.fail('My custom failure message', {name: 'My custom test-case name' });
```
will produce the following xml.

```xml
<?xml version="1.0" encoding="UTF-8"?>
<testsuites time="0.383">
	<testsuite errors="0" failures="1" name="demo" package="./custom-test-case-name" tests="1" time="0.383" timestamp="2014-07-04T11:09:11.072Z">
		<testcase classname="./custom-test-case-name" name="My custom test-case name" time="0.165">
			<failure type="fail">My custom failure message</failure>
		</testcase>
		<system-out/>
	</testsuite>
</testsuites>
```

What do you think about it guys?

best regards
~david