Remove consistency group volumes form exception redict url error.

Env: devstack master branch
When submit remove consistency group volumes and execute exception,
it will throws an exception.

Exception info:
Internal Server Error: /project/cgroups/aa1c9791-0878-4aa1-bd4a-52658ff909c5/remove_volumese/
Traceback (most recent call last):
  File "/usr/local/lib/python2.7/dist-packages/django/core/handlers/base.py", line 132, in get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "/opt/stack/horizon/horizon/decorators.py", line 36, in dec
    return view_func(request, *args, **kwargs)
  File "/opt/stack/horizon/horizon/decorators.py", line 52, in dec
    return view_func(request, *args, **kwargs)
  File "/opt/stack/horizon/horizon/decorators.py", line 36, in dec
    return view_func(request, *args, **kwargs)
  File "/opt/stack/horizon/horizon/decorators.py", line 84, in dec
    return view_func(request, *args, **kwargs)
  File "/usr/local/lib/python2.7/dist-packages/django/views/generic/base.py", line 71, in view
    return self.dispatch(request, *args, **kwargs)
  File "/usr/local/lib/python2.7/dist-packages/django/views/generic/base.py", line 89, in dispatch
    return handler(request, *args, **kwargs)
  File "/usr/local/lib/python2.7/dist-packages/django/views/generic/edit.py", line 215, in post
    return self.form_valid(form)
  File "/opt/stack/horizon/horizon/forms/views.py", line 180, in form_valid
    exceptions.handle(self.request)
  File "/opt/stack/horizon/horizon/exceptions.py", line 352, in handle
    six.reraise(exc_type, exc_value, exc_traceback)
  File "/opt/stack/horizon/horizon/forms/views.py", line 177, in form_valid
    handled = form.handle(self.request, form.cleaned_data)
  File "/opt/stack/horizon/openstack_dashboard/dashboards/project/cgroups/forms.py", line 88, in handle
    redirect = reverse("horizon:project:groups:index")
  File "/usr/local/lib/python2.7/dist-packages/django/core/urlresolvers.py", line 571, in reverse
    (key, ':'.join(resolved_path)))
NoReverseMatch: u'groups' is not a registered namespace inside 'horizon:project'