Make get-apres and delete-apires more efficient

[morningspace]

get-apires and delete-apires is very helpful when you want to clean up resources in a namespace before you delete the namespace, otherwise, it's very easy to lead to the deleted namespace keeping in terminating status.

But the current implementation will have iterator each api-resource inside the namespace one by one, and in order to get the number of instances being processed for each resource, it make an call against the resource, so there will be twice kubectl calls for each resource. This makes the overall run a bit slow.

Also, it prints message even there's no instances for a particular resource. In some cases, it may be a bit annoying if I just want to know which resources really have instances and are processed.