时区表：TTZZ
function：
TZON_GET_OS_TIMEZONE - returns the timezone of your machine, then use it in
ISU_DATE_TIME_CONVERT_TIMEZONE - return your local time.
sap help：
http://help.sap.com/saphelp_470/helpdata/en/fe/1ddeac104311d3a54f444553540000/content.htm