Introduce bash completions for kubecfg

completions only work for list, get, create, delete.
Yes, once I managed to collapse it to a single caller to kubecfg it seemed ok to drop the function.   I strongly dislike the 2>/dev/null scattered throughout.  It's just too easy to get wrong.  (we missed it in a couple of places in hack/, but they've since been cleaned up.

Hard to get it wrong though when we only need it once   :)