change response.redirected_to to response.should redirect_to for rails 3

Change-Id: I919e9f1eee81c972baa97832a6599fbb340eb82d
Reviewed-on: https://gerrit.instructure.com/29805
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: James Williams  <jamesw@instructure.com>
Product-Review: Cody Cutrer <cody@instructure.com>
QA-Review: Cody Cutrer <cody@instructure.com>