Add easy setup for simple controller

Also add tests; coverage up to 86.7%

pkg/client/cache/store.go

@@ -59,6 +59,10 @@ func (k KeyError) Error() string {
 	return fmt.Sprintf("couldn't create key for object %+v: %v", k.Obj, k.Err)
 }
 
+// ExplicitKey can be passed to MetaNamespaceKeyFunc if you have the key for
+// the object but not the object itself.
+type ExplicitKey string
+
 // MetaNamespaceKeyFunc is a convenient default KeyFunc which knows how to make
 // keys for API objects which implement meta.Interface.
 // The key uses the format <namespace>/<name> unless <namespace> is empty, then