Switch usage of request.ip to request.remote_ip
We allow configuration of trusted_proxies in gitlab.yml, which configures action_dispatch's trusted proxies. This impacts request.remote_ip but not request.ip.
While it looks like gems like devise are already using remote_ip (see https://github.com/plataformatec/devise/blob/master/lib/devise/models/trackable.rb#L23, thanks @grzesiek )
GitLab is currently passing request.ip in https://gitlab.com/gitlab-org/gitlab-ce/blob/master/lib/gitlab/backend/grack_auth.rb#L122 and soon https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/3787
cc\ @ayufan