[WIP] Add selector filter to 'cli delete' cmd

Most of these changes will probably go UPSTREAM, unless I'm proven wrong. Let's discuss here first.

@smarterclayton @fabianofranz feedback would be appreciated.

- [x] `openshift cli delete -l template=guestbook-example pods redis-master`
- [ ] `openshift cli delete -l template=guestbook-example pods`
- [ ] `openshift cli delete -l template=guestbook-example pods,services`
I need to filter first, as seen above, unless I want to add `labels` as parameter to every `Delete()` implementation of the RESTStorage interface. Is this a good way?