Add comment as user for one or more datasets

def marvcli_comment_add(user, message, datasets):
    """Add comment as user for one or more datasets"""
    app = create_app()
    try:
        db.session.query(User).filter(User.name==user).one()
    except NoResultFound:
        click.echo("ERROR: No such user '{}'".format(user), err=True)
        sys.exit(1)
    ids = parse_setids(datasets, dbids=True)
    app.site.comment(user, message, ids)