Change the username for a named user

    CLI Example:

    .. code-block:: bash

        salt '*' user.rename name new_name

def rename(name, new_name):
    '''
    Change the username for a named user

    CLI Example:

    .. code-block:: bash

        salt '*' user.rename name new_name
    '''
    current_info = info(name)
    if not current_info:
        raise CommandExecutionError('User \'{0}\' does not exist'.format(name))
    new_info = info(new_name)
    if new_info:
        raise CommandExecutionError(
            'User \'{0}\' already exists'.format(new_name)
        )
    cmd = ['usermod', '-l', new_name, name]
    __salt__['cmd.run'](cmd, python_shell=False)
    return info(new_name).get('name') == new_name