spec: fix auditor spec regressions

undo the change in f42af73 ... since we were reusing models but not
clearing out cassandra, one spec could interfere with another

Change-Id: Iae606575ce53f54e6659159e49a6e79a42e42ae5
Reviewed-on: https://gerrit.instructure.com/37161
Reviewed-by: Cody Cutrer <cody@instructure.com>
Product-Review: Jon Jensen <jon@instructure.com>
QA-Review: Jon Jensen <jon@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>