spec: fix external_tools_controller_spec in rails3

Change-Id: Iab9cdcead5036b18542cb02720057b62ab103cd2
Reviewed-on: https://gerrit.instructure.com/29970
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>