ensure a consistent ordering in web conferences api

refs CNVS-7032

Change-Id: I934c87defd9fccc4ea35a73e4bc7c541b5769217
Reviewed-on: https://gerrit.instructure.com/28601
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Nick Cloward <ncloward@instructure.com>
QA-Review: Cody Cutrer <cody@instructure.com>
Product-Review: Cody Cutrer <cody@instructure.com>