Set 404 cache control header.
Set 404 cache control header.

Set Cache-Control headers on 404 pages since we overide those set by
apps. So that we dont fall through to the default provided by the CDN.

alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet