fix query translation of imported external tools

test plan:
* import the package referenced in #CNVS-13144
* launch the external tool module item "title 1"
* inspect the form element on the launch page
* the url should have query parameters with
 "custom_" prepended to them

(e.g. "http://www.example.com/testlti?custom_resource_url=...")

closes #PLAT-584

Change-Id: I0d70244b78b6fc36ec188429a1ea7ccc4094bc70
Reviewed-on: https://gerrit.instructure.com/38799
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Brad Humphrey <brad@instructure.com>
Product-Review: Bracken Mosbacker <bracken@instructure.com>
QA-Review: Clare Strong <clare@instructure.com>