spec: reset default shard before running

Change-Id: Ia2f6e58d1fcbf00054e86d3da2aa4e2f6364aa77
Reviewed-on: https://gerrit.instructure.com/37662
Reviewed-by: Cody Cutrer <cody@instructure.com>
Reviewed-by: Brian Palmer <brianp@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
Product-Review: James Williams  <jamesw@instructure.com>
QA-Review: James Williams  <jamesw@instructure.com>