Unit testing when using namespaces failing

### Expected Behaviour

In an application using namespaces for controllers, unit testing a redirect should work fine.
### Actual Behaviour

unit testing redirects does not generate the proper url when using namespaces
### Environment Information
- **Operating System**: Mac OS X 10.11.6
- **Grails Version:** 3.1.10
- **JDK Version:** 1.8.0_92
### Example Application
- https://github.com/frangarcia/errortestapp

This is an example project to show an issue when unit testing redirect on grails controllers when using namespaces.

After starting up the grails application with the command:

```
grails run-app
```

and going to http://localhost:8080/admin/content, it redirects to http://localhost:8080/admin/content/list, which is the expected behaviour.

The problem comes with the unit test ContentControllerSpec not working as expected, so when running

```
grails test-app -unit
```

the error does not pass because the application does not do the redirection properly

Start with the linked errortestapp and its ContentControllerSpec, then run `grails test-app -unit` to reproduce the namespace redirect failure. Compare the unit-test redirect with the behavior from `grails run-app` at `/admin/content`, where the expected destination is `/admin/content/list`; done means the test passes with the proper namespaced URL.

Written by the indexing model from the issue text.