CLI action "run editor for blacklist".

def do_blacklist(config, config_dir):
    """
    CLI action "run editor for blacklist".
    """
    if not os.path.exists(config_dir):
        print "Configuration '{}' does not exist.".format(config)
        exit(1)    

    editor = os.environ["EDITOR"]

    config_blacklist = os.path.join(config_dir, 'blacklist')
    call([editor, config_blacklist])
    print "Blacklist configuration has been updated."