Convert expansions from !OLD! style to {new}.

def convert_old_command_expansions(command):
    """Convert expansions from !OLD! style to {new}."""
    command = command.replace("!VERSION!",       "{version}")
    command = command.replace("!MAJOR_VERSION!", "{version.major}")
    command = command.replace("!MINOR_VERSION!", "{version.minor}")
    command = command.replace("!BASE!",          "{base}")
    command = command.replace("!ROOT!",          "{root}")
    command = command.replace("!USER!",          "{system.user}")
    return command