Added support for processed job status in event nr2

This PR supersedes #83 as I am making tests pass again, applying some changed discussed in #83 and creating tests for this new feature.
Mm, I am not sure if this is the implementation @stefankleff meant, but here I am allowing to return the status of the job itself. This is the easiest for this test. I am implementing it in the adapter so jobs can return status codes or else the worker returns success/failure. See juriansluiman/SlmQueueBeanstalkd#38 for an example implementation.