Get root container stats from cAdvisor

I changed the GetContainerStats function, which will return the root container's stats if the container name is empty. This is useful when the master wants to know machine wide information. e.g. total memory usage of a certain node.
Agreed.  Sorry, I keep conflating pod and container in my mind.  Whenever I say 'container' I think its safe to assume that I actually mean 'pod'

Sooner or later I will learn how to speak ;)