converts context/new_roster_user js_block into js_bundle

test plan:
* regression test context new roster user

Change-Id: Ia3ce1cb8102776578ecab5a4ff0cb64112e44cf7
Reviewed-on: https://gerrit.instructure.com/29162
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Matt Fairbourn <mfairbourn@instructure.com>
Reviewed-by: Landon Wilkins <lwilkins@instructure.com>
Product-Review: Landon Wilkins <lwilkins@instructure.com>