kuryr-manage cli tool

We need a kuryr-manage cli tool. This tool should work with subcommands. The first one to add is the subports command:

    kuryr-manage subports list - Lists the subports managed by Kuryr-kubernetes
    kuryr-manage subports free - Deletes all the subports managed by kuryr-kubernetes

The implementation should be usable both from Python as in:

from kuryr_kubernetes.manage import lib

    lib.subports.list()
    lib.subports.free()

and from the command line as described above.