spec: add get_options for a combo box

Change-Id: Ibf929a68ed7e2085e19505da86de307a7bf5642d
Reviewed-on: https://gerrit.instructure.com/43286
Reviewed-by: Adam Ard <aard@instructure.com>
QA-Review: Adam Ard <aard@instructure.com>
Product-Review: Adam Ard <aard@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>