Return exit code 0 instead of 2 when examples are skipped

Skipping examples should not make the spec suite fail (which is the case today).

I've updated the behat step to actually check the application exit code. (Related issue: https://github.com/phpspec/phpspec/issues/315)
@stof I think status is fine. It's more commonly referred to as an exit status, if anything. Even [PHP's documentation](http://php.net/manual/en/function.exit.php) refers to it as a status. I know Symfony calls it an exit code, though.