Add method_existe() to TestListener to avoid mask test errors

I was getting this error:

```
Fatal error: Call to undefined method PHPUnit_Framework_TestSuite::addToAssertionCount() in /private/var/www/uniplaces/vendor/mockery/mockery/library/Mockery/Adapter/Phpunit/TestListener.php on line 39
```

When added a method_exists start getting the real error:
```
1) Uniplaces\AccommodationBundle\Tests\Functional\AccommodationOffer\AccommodationOfferCommandControllerTest
exception 'RuntimeException' with message 'OUTPUT: 
Catchable fatal error: Argument 2 passed to Uniplaces\Library\Controller\CommandController::__construct() must implement interface Symfony\Component\Security\Core\SecurityContextInterface, none given, called in /private/var/www/uniplaces/src/Uniplaces/UserBundle/Application/Session/Controller/SessionCommandController.php on line 33 and defined in /private/var/www/uniplaces/vendor/uniplaces/uniplaces-library/src/Unip
```

Adding this method_exists allow to see the real error.