rails3: revert to rails2 behavior for exceptions in tests

Change-Id: If8969692bfe2e3cce63ca7bd6a56b8356cb725aa
Reviewed-on: https://gerrit.instructure.com/30282
Reviewed-by: Brian Palmer <brianp@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
Product-Review: Cameron Matheson <cameron@instructure.com>
QA-Review: Cameron Matheson <cameron@instructure.com>