KnoxCLI For Listing Provider Configurations and Descriptors in a Remote Configuration Registry

KNOX-1125 introduced Knox CLI commands for adding and removing provider configurations and simple descriptors to a remote configuration registry (e.g., ZooKeeper). It would be helpful to also have the ability to list the provider configurations and descriptors that are in the registry.

list-provider-configs --registry-client name
list-descriptors --registry-client name