disable reloading of periodic jobs config in development mode

This fixes issues when class caching is disabled. Canvas will need to be
restarted to pick up changes to this file.

Change-Id: Ief4c171df7b31e6264b9bf370d404ae21d827b4d
Reviewed-on: https://gerrit.instructure.com/43381
Reviewed-by: Ryan Taylor <rtaylor@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Brian Palmer <brianp@instructure.com>
Product-Review: Brian Palmer <brianp@instructure.com>