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.
I tried. path.Clean() is useful, but we still need to drop empty strings if the path is an absolute path, i.e. "/some/thing". See here: http://play.golang.org/p/E1nOyi3SFP