fix sis/user_importer_spec for rails 3

also make sure that _stub_sleep doesn't remain if
the spec fails

Change-Id: I355cf5623285492131b01f45eb7e1a800635255a
Reviewed-on: https://gerrit.instructure.com/30993
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Cody Cutrer <cody@instructure.com>
Product-Review: James Williams  <jamesw@instructure.com>
QA-Review: James Williams  <jamesw@instructure.com>