title: reverse for success_url on Django Class Based View complain about circular import
body: <p>When using method-based view, redirecting with <code>reverse</code> didn't complain about this and can still find the root url conf. But, in class-based views, it complain:</p>
  
  <pre><code>ImproperlyConfigured at /blog/new-post/
  
  The included urlconf 'blog.urls' does not appear to have any
  patterns in it. If you see valid patterns in the file then the
  issue is probably caused by a circular import.
  </code></pre>
  
  <p>My class is defined like this:</p>
  
  <pre><code>class BlogCreateView(generic.CreateView):
      form_class = Blog
      template_name = 'blog/new-post.html'
      success_url = reverse('blog:list-post')
  </code></pre>
  
  <p>How to properly use <code>reverse</code> for <code>success_url</code> in class-based views? Thanks.</p>
  
  <p><strong>PS:</strong> And I'm interested in why it's need to restart <code>runserver</code> after this error (not like an error like <code>TemplateDoesNotExists</code> which is no need to restart <code>runserver</code>)</p>