When I run "rke up", I see following error:

WARN[0010] Can't pull Docker image [<image in our private registry>] on host [<hostname>]:  Error response from daemon: Get <image in our private registry>: uknown: Authentication is required

However, if I ssh to that <hostname>, and run following command as root:

docker pull <image in our private registry>

Everything is fine. Some insight?