expanding command module to handle rc_{ok,changed,failed}

Hello, this is a PR for the rc modifications to the command module.

I'm currently stuck on is_succesful from lib/ansible/runner/return_data.py
Is it possible to get it the list of non-failing rc's.

Will I need to add the rc logic to runner so it can parse what is successful from module_args?

    def is_successful(self, rc_ok = [0]):
        return self.comm_ok and (self.result.get('failed', False) == False) and (self.result.get('rc',0) in rc_ok)


I started a gist of my testing [here](https://gist.github.com/fdavis/4751195).