spec: make sure mocking is configured for swagger

fixes CNVS-10649

otherwise rspec 2 in rails 3 will complain about changing the
mocking after defining some example groups when running swagger specs
with other specs

Change-Id: I68a690789300f5a0bb620d6d5171432fa678a84e
Reviewed-on: https://gerrit.instructure.com/29070
Tested-by: Jenkins <jenkins@instructure.com>
Product-Review: Bryan Madsen <bryan@instructure.com>
QA-Review: Bryan Madsen <bryan@instructure.com>
Reviewed-by: Jacob Fugal <jacob@instructure.com>