fix content importers without class caching

Change-Id: Ifad2fdbaac327cdaac985a0a10afd09e7c136208
Reviewed-on: https://gerrit.instructure.com/37910
Reviewed-by: Jeremy Stanley <jeremy@instructure.com>
Product-Review: Jeremy Stanley <jeremy@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: James Williams  <jamesw@instructure.com>