fix find_in_batches_with_temp_table on mysql to not commit the transaction

Change-Id: I1d4207506173cd1c84c4ac31e6ea6b54d42860da
Reviewed-on: https://gerrit.instructure.com/28526
Reviewed-by: Rob Orton <rob@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Cody Cutrer <cody@instructure.com>
Product-Review: Cody Cutrer <cody@instructure.com>