Console exception

Hey, I've fixed a typo in this (was calling the wrong method) and added a test.

> PHP Warning:  call_user_func() expects parameter 1 to be a valid callback, class 'Ekino\Bundle\NewRelicBundle\Listener\CommandListener' does not have a method 'onKernelException' in .../vendor/symfony/symfony/src/Symfony/Component/EventDispatcher/EventDispatcher.php on line 164

ref ekino/EkinoNewRelicBundle#30