converts external_tools/tool_show js_block into js_bundle

test plan:
* regression test external tools (tool show)

Change-Id: I06e8ade221fe826a378206e819dd6457ece667fe
Reviewed-on: https://gerrit.instructure.com/29151
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Stanley Stuart <stanley@instructure.com>
QA-Review: Matt Fairbourn <mfairbourn@instructure.com>
Product-Review: Landon Wilkins <lwilkins@instructure.com>