Instantiate cAdvisor client for kubelet

With this PR, Kubelet can query machine, pod, and container(s) resource information. The following PRs will enable the support to retrieve such info through apiserver URI. 
idiomatically I think this should be:

if kl.CadvisorClient, err := cadvisor.NewClient("http://127.0.0.1:5000"); err != nil {
    glog.Errorf("Error on creating cadvisor client: %v", err)
}

I would also argue that 127.0.0.1 be replaced with "localhost"