Add a server:port member to a servicegroup

    CLI Example:

    .. code-block:: bash

        salt '*' netscaler.servicegroup_server_add 'serviceGroupName' 'serverName' 'serverPort'

def servicegroup_server_add(sg_name, s_name, s_port, **connection_args):
    '''
    Add a server:port member to a servicegroup

    CLI Example:

    .. code-block:: bash

        salt '*' netscaler.servicegroup_server_add 'serviceGroupName' 'serverName' 'serverPort'
    '''
    # Nitro will throw an error if the server is already present
    ret = True
    server = _servicegroup_get_server(sg_name, s_name, s_port, **connection_args)
    if server is not None:
        return False
    nitro = _connect(**connection_args)
    if nitro is None:
        return False
    sgsb = NSServiceGroupServerBinding()
    sgsb.set_servicegroupname(sg_name)
    sgsb.set_servername(s_name)
    sgsb.set_port(s_port)
    try:
        NSServiceGroupServerBinding.add(nitro, sgsb)
    except NSNitroError as error:
        log.debug('netscaler module error - NSServiceGroupServerBinding() failed: %s', error)
        ret = False
    _disconnect(nitro)
    return ret