clear schema information during db:test:reset

Change-Id: I3fb4e3df3bf8a7d305cb27d4e79e8454580f9c2a
Reviewed-on: https://gerrit.instructure.com/29676
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Jon Willesen <jonw@instructure.com>
Product-Review: Cody Cutrer <cody@instructure.com>
QA-Review: Cody Cutrer <cody@instructure.com>