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. 
On Tue, Jul 8, 2014 at 9:47 PM, Tim Hockin <notifications@github.com> wrote:

> In pkg/kubelet/kubelet.go:
>
> > @@ -108,6 +109,13 @@ const (
> >  // Starts background goroutines. If config_path, manifest_url, or address are empty,
> >  // they are not watched. Never returns.
> >  func (kl *Kubelet) RunKubelet(dockerEndpoint, config_path, manifest_url, etcd_servers, address string, port uint) {
> > +	if kl.CadvisorClient == nil {
> > +		var err error
> > +		kl.CadvisorClient, err = cadvisor.NewClient("http://127.0.0.1:5000")
>
> I just realized that field init does not work with := assignment. Sigh. Go.
>
Yeah, learnt it today too. :-)


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