Manage the authentication keys with salt-key.

def salt_key():
    '''
    Manage the authentication keys with salt-key.
    '''
    import salt.cli.key
    try:
        client = salt.cli.key.SaltKey()
        _install_signal_handlers(client)
        client.run()
    except Exception as err:
        sys.stderr.write("Error: {0}\n".format(err))