Kubectl namespace support

Added support for setting a namespace for kubectl requests.

FYI @ghodss 
Good point.  I will make an update. 

Sent from my iPhone

> On Oct 22, 2014, at 3:18 PM, Sam Ghods <notifications@github.com> wrote:
> 
> In pkg/kubectl/cmd/namespace.go:
> 
> > +)
> > +
> > +func NewCmdNamespace(out io.Writer) *cobra.Command {
> > +	cmd := &cobra.Command{
> > +		Use:   "namespace [<namespace>]",
> > +		Short: "Set and view the current Kubernetes namespace",
> > +		Long: `Set and view the current Kubernetes namespace scope for command line requests.
> > +
> > +A Kubernetes namespace subdivides the cluster into groups of logically related pods, services, and replication controllers.
> > +
> > +Examples:
> > +  $ kubectl namespace 
> > +  Using namespace default
> > +
> > +  $ kubectl namespace other
> > +  Using namespace other`,
> It would be nice if there was some slightly different language for when the namespace is set vs is just being displayed. Since "default" is the namespace used when none is provided, it's not entirely clear that kubectl namespace Using namespace default isn't actually also setting it to default/clearing the value.
> 
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