spec: rails3 group category spec

Change-Id: I00e5b38cbeccae41fddbd73366f0173e0bce0595
Reviewed-on: https://gerrit.instructure.com/29960
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Cody Cutrer <cody@instructure.com>
Product-Review: Jon Willesen <jonw@instructure.com>
QA-Review: Jon Willesen <jonw@instructure.com>