Submit to external tool form url built with ENV.COURSE_ID

Fixes PLAT-306

Change-Id: I61a77bdf7f05670d91ea03cecbe049076306d748
Reviewed-on: https://gerrit.instructure.com/28619
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Brad Humphrey <brad@instructure.com>
QA-Review: Nathan Rogowski <nathan@instructure.com>
Product-Review: Eric Berry <ericb@instructure.com>