use dup instead of clone for active record in rails 3

Change-Id: Ia718f317d2528e0382a3c10f9d2b6de423195479
Reviewed-on: https://gerrit.instructure.com/28219
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Jacob Fugal <jacob@instructure.com>
Reviewed-by: Cody Cutrer <cody@instructure.com>
QA-Review: James Williams  <jamesw@instructure.com>
Product-Review: James Williams  <jamesw@instructure.com>