Have logstash be less verbose on 404 errors.

Change-Id: Ie6905039d4752d578566861ffd340cf607ad270b
Reviewed-on: https://review.openstack.org/32819
Reviewed-by: Jeremy Stanley <fungi@yuggoth.org>
Reviewed-by: Khai Do <zaro0508@gmail.com>
Approved: Clark Boylan <clark.boylan@gmail.com>
Reviewed-by: Clark Boylan <clark.boylan@gmail.com>
Tested-by: Jenkins