Add gitlab-runner binary to www-gitlab-com

This request will add the `gitlab-runner` binary to the www-gitlab-com image. This is required to make CI work on a kubernetes cluster. 

This is a workaround for https://gitlab.com/gitlab-org/gitlab-ci-multi-runner/issues/1908 and is needed for https://gitlab.com/gitlab-com/infrastructure/issues/749

See merge request !19