add scope to allow selection of placements

fixes PLAT-656

test
*specs pass

Change-Id: I824bb17df3d20c89224d453c858237969a869a24
Reviewed-on: https://gerrit.instructure.com/41785
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Brad Humphrey <brad@instructure.com>
Product-Review: Nathan Mills <nathanm@instructure.com>
QA-Review: Nathan Mills <nathanm@instructure.com>