Flush MQ after tests

To avoid errors like

```
[2013-03-12T11:28:42.788Z] ERROR: oae-preview-processor/99820 on Nicolaass-MacBook-Pro.local: Got an unexpected error from the REST api.
    err: {
      "code": 404,
      "msg": "There is no tenant with alias camtest"
    }
[2013-03-12T11:28:42.789Z] ERROR: oae-preview-processor/99820 on Nicolaass-MacBook-Pro.local: We could not log in on the the tenant. The status of the content item will not be set. (contentId=c:camtest:VTvsW1BmHf)
    err: {
      "code": 404,
      "msg": "There is no tenant with alias camtest"
    }
```