make cc converter file search more flexible

test plan:
* import the package referenced in the ticket
 as a common cartidge package
* the migration should not generate missing
file reference warnings

closes #CNVS-14681

Change-Id: I762a51c63a9b55847914ce10e022524b030e3c1b
Reviewed-on: https://gerrit.instructure.com/39101
Reviewed-by: Jeremy Stanley <jeremy@instructure.com>
Product-Review: Jeremy Stanley <jeremy@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Clare Strong <clare@instructure.com>