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)
this should be done in the RunCommand only IMO (other commands are not expected to have anything to do with a test result, but already with exit codes)