fix external feed iteration through bouncer

Change-Id: Ia4798b064d845efe9a134e1e2125d80826157b61
Reviewed-on: https://gerrit.instructure.com/39946
Reviewed-by: Cody Cutrer <cody@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
Product-Review: Brian Palmer <brianp@instructure.com>
QA-Review: Brian Palmer <brianp@instructure.com>