isinstall update local cache only with -u

# Top level argument parsing

p_main = argparse.ArgumentParser()

p_main.add_argument("-v", "--version", action="version", version=installsystems.version,

p_main.add_argument("-", "--version", action="version", version=installsystems.version,

                    help="show installsystems version")

p_main.add_argument('-d', "--debug", action=DebugAction, nargs=0,

                    help="active debug mode")

                    help="specific image version")

p_main.add_argument("image_name", type=str,

                    help="image to install")

p_main.add_argument('-u', "--update", action="store_true", dest="update", default=False,

                    help="update repository cache")

# program entry point

try:

    # register command ligne repo

    if args.image_path is not None:

        repocache.register("cmdline", args.image_path, args.data_path)

    # update remote info if available

    # update remote info if -u options is present

    if args.update:

        repocache.update()

    # get image package

    pkg = repocache.get(args.image_name, args.image_version)