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)
Well, in all man pages I read, I saw ``exit code`` being used, not ``status code``.

I think the naming in the PHP documentation is a confusion with the HTTP status code