don't bother checking redis in a health check

we automatically work around redis failures anyway

Change-Id: I13c8b689447ee1de27a768d442624d2839a52ea1
Reviewed-on: https://gerrit.instructure.com/39980
Reviewed-by: Brian Palmer <brianp@instructure.com>
Reviewed-by: Jacob Fugal <jacob@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
Product-Review: Cody Cutrer <cody@instructure.com>
QA-Review: Cody Cutrer <cody@instructure.com>