spec: make bookmarked collection spec more tolerant of non-empty db

Change-Id: I2495f415461194880e37d487cedcab346976f4bc
Reviewed-on: https://gerrit.instructure.com/28978
Reviewed-by: Brian Palmer <brianp@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
Product-Review: Cody Cutrer <cody@instructure.com>
QA-Review: Cody Cutrer <cody@instructure.com>