<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:

def set_config(variable, value):
    '''
    Set the value of a Traffic Server configuration variable.

    variable
        Name of a Traffic Server configuration variable.

    value
        The new value to set.

    .. versionadded:: 2016.11.0

    .. code-block:: bash

        salt '*' trafficserver.set_config proxy.config.http.keep_alive_post_out 0
    '''

    if _TRAFFICCTL:
        cmd = _traffic_ctl('config', 'set', variable, value)
    else:
        cmd = _traffic_line('-s', variable, '-v', value)

    log.debug('Setting %s to %s', variable, value)
    return _subprocess(cmd)