Bump system-docker from 17.06-ros4 to 17.06-ros6

Author: niusmallnan

Dockerfile.dapper

@@ -82,9 +82,9 @@ ARG DFS_IMAGE=${OS_REPO}/docker:v${DOCKER_VERSION}-2
 ARG OS_BASE_URL_amd64=https://github.com/rancher/os-base/releases/download/v2018.02-4/os-base_amd64.tar.xz
 ARG OS_BASE_URL_arm64=https://github.com/rancher/os-base/releases/download/v2018.02-4/os-base_arm64.tar.xz
 
-ARG SYSTEM_DOCKER_VERSION=17.06-ros4
-ARG SYSTEM_DOCKER_URL_amd64=https://github.com/rancher/os-system-docker/releases/download/${SYSTEM_DOCKER_VERSION}/docker-amd64-${SYSTEM_DOCKER_VERSION}.tgz
-ARG SYSTEM_DOCKER_URL_arm64=https://github.com/rancher/os-system-docker/releases/download/${SYSTEM_DOCKER_VERSION}/docker-arm64-${SYSTEM_DOCKER_VERSION}.tgz
+ARG SYSTEM_DOCKER_VERSION=17.06-ros6
+ARG SYSTEM_DOCKER_URL_amd64=https://releases.rancher.com/os/system-docker/docker-amd64-${SYSTEM_DOCKER_VERSION}.tgz
+ARG SYSTEM_DOCKER_URL_arm64=https://releases.rancher.com/os/system-docker/docker-arm64-${SYSTEM_DOCKER_VERSION}.tgz
 
 ARG VMWARE_AUTOFORMAT=1
 ARG OPEN_VMTOOLS_VERSION=10.2.5-3