pkgrepo.managed should return True if repo is already configured

Currently when configuring a repo, the output will be the following on a first (successful) run
```
----------
    State: - pkgrepo
    Name:      deb http://ceph.com/debian-cuttlefish/ raring main
    Function:  managed
        Result:    True
        Comment:   Configured package repo deb http://ceph.com/debian-cuttlefish/ raring main
        Changes:   repo: deb http://ceph.com/debian-cuttlefish/ raring main
```

However on subsequent runs, the output will have a `Result: none`
```
----------
    State: - pkgrepo
    Name:      deb http://ceph.com/debian-cuttlefish/ raring main
    Function:  managed
        Result:    None
        Comment:   Package repo deb http://ceph.com/debian-cuttlefish/ raring main already configured
        Changes:   
```

I believe that we want to return `Result: True` when the repo is already configured to indicate that the state is in a good state.

I have included a pull request. This has been tested on `Ubuntu 13.04` only.