update app status in content ratings pingback api (bug 945265)

After couple hours looking and with little way to test locally, just gave up with the ```post_save``` working and am just manually updating the status in the API.

**Debugging Notes**

- ContentRating has a post_save to update the app status.
- set_content_ratings calls ContentRating.safer_get_or_create, which calls the post_save.
- calling set_content_ratings in the shell updates the app's status, for a submitted app that hasn't yet gotten content rating.
- tests on the pingback API correctly update the status
- the actual pingback API sets the content ratings, but fails to update the status