Authenticated docker pulls, pt. I

The simplest reasonable thing to do here is to read the `.dockercfg` files that are already available to the kubelets. This only happens on startup, so any changes the user makes  to `.dockercfg` will only be applied after a service restart.
Can you comment on why this function does all this work? And why it then discards it?  Wouldn't you be better off saving the results?