fix most assignments controller specs in rails 3

Change-Id: Ib96144c0cdd4be1c9599dd722cfaa7d9fcd1cdcf
Reviewed-on: https://gerrit.instructure.com/29778
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Ryan Florence <ryanf@instructure.com>
Product-Review: Cody Cutrer <cody@instructure.com>
QA-Review: Cody Cutrer <cody@instructure.com>