Support provided argument list instead of sys.argv to make it easier …

[thors]

…to wrap the cli

Example of how I'd like to implement a wrapper:

    ap = argparse.ArgumentParser()
    ap.add_argument('--tag_dimension', default=[], action='append', help='EC2 instance tags to add')
    ap.add_argument('--dimensions', default="", help='fixed dimensions')
    (myargs,restargs) = ap.parse_known_args()
    new_dimensions=""
    for tag in myargs.tag_dimension:
        new_dimensions="," + tag + "=" + get_tag_value(tag)
    if len(myargs.dimensions) > 0:
        myargs.dimensions = myargs.dimensions + new_dimensions
    else:
        myargs.dimensions = new_dimensions[1:]
    if len(myargs.dimensions) > 0:
        restargs = ["--dimensions",myargs.dimensions] + restargs
    n2cw.cli.cli(restargs)