converts context/roster_user js_block into js_bundle

test plan:
* regression test context roster user

Change-Id: I98a175ae3a2724cef8e990360f77d23fa1065014
Reviewed-on: https://gerrit.instructure.com/29161
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Jon Jensen <jon@instructure.com>
QA-Review: Steven Shepherd <sshepherd@instructure.com>
Product-Review: Landon Wilkins <lwilkins@instructure.com>