Do not duplicate error, reported in request context

Change-Id: Iabc40ee73dce82c547114bad9db397a7ea7536b8
Reviewed-on: http://review.couchbase.org/29918
Tested-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Reviewed-by: Mark Nunberg <mnunberg@haskalah.org>