spec: gradebook2 data setup refactor

Change-Id: Ieb06d22b70e1103a3c7b93e60149ee73a90b532d
Reviewed-on: https://gerrit.instructure.com/42854
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Adam Ard <aard@instructure.com>
Product-Review: Adam Ard <aard@instructure.com>
QA-Review: Adam Ard <aard@instructure.com>