improved proxy support

cluster.yml

roles/docker/tasks/main.yml

roles/download/tasks/download_container.yml

roles/download/tasks/download_file.yml

roles/kubernetes-apps/helm/templates/helm-container.j2

roles/kubernetes/preinstall/tasks/main.yml

roles/rkt/tasks/install.yml

roles/vault/tasks/cluster/systemd.yml

roles/vault/templates/http-proxy.conf.j2