update relative_id_for to switchman style

Change-Id: I0bc5b04d6210c90aa607e23714e7e78a2964e8ff
Reviewed-on: https://gerrit.instructure.com/29517
Reviewed-by: Cody Cutrer <cody@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
Product-Review: James Williams  <jamesw@instructure.com>
QA-Review: James Williams  <jamesw@instructure.com>