A lot of packages use StringSet, but they don't use anything else from
the util package. Moving StringSet into another package will shrink
their dependency trees significantly.
kubectl get can output a series of objects as a List in versioned
form, but not all API objects are available in the same schema.
Make the act of converting a []runtime.Object to api.List more
robust and add a test to verify its behavior in Get.
Makes it easier for client code to output unified objects.
