use select_all, not execute

execute has an undefined return type that varies by adapter

refs CNVS-7032

Change-Id: Ia3004cf743afb038ad522588d1ad5d3b0fa9ebe5
Reviewed-on: https://gerrit.instructure.com/28616
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Nick Cloward <ncloward@instructure.com>
QA-Review: Cody Cutrer <cody@instructure.com>
Product-Review: Cody Cutrer <cody@instructure.com>