Adding capability to delete resources via label selector

@smarterclayton, @bgrant0607  @derekwaynecarr Thanks to have a look when you have time

See #2438 for motivation.
Yes, but the "all" function is broken if there are more resources than what Kube provides, whereas there are just no shortcuts for non cube resources.  Fixing both is great.

----- Original Message -----
> > +	for _, arg := range args {
> > +		if arg == "all" {
> > +			extractedArgs = append(extractedArgs, GetAllResources()...)
> > +			continue
> > +		}
> > +		for _, value := range strings.FieldsFunc(arg, isComma) {
> > +			extractedArgs = append(extractedArgs, value)
> > +		}
> > +	}
> > +
> > +	RemoveDuplicates(&extractedArgs)
> > +	return extractedArgs
> > +}
> > +
> > +// GetAllResources will return the full list of handled resources.
> > +// TODO: Combine with RESTMapper stuff to provide a general solution
> 
> @smarterclayton isn't this also true for func ExpandResourceShortcut(resource
> string) string in kubectl.go?
> 
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> https://github.com/GoogleCloudPlatform/kubernetes/pull/2684/files#r21163775