Sorry, but without 
```
raise StopIteration
```
it doesn't work right, when nailgun starts downloading he sends serveral tasks in an array something like
[check_credentials, check_licenses, download_redhat]
so, if check_credentials was failed it will be handled [here](https://github.com/Mirantis/fuelweb/blob/master/naily/lib/naily/server.rb#L75) and aborted next tasks.
Yes, it's a bad design, should we fix it? Yes. Should we fix it right now? I don't know.