修改MySQL日志记录时间为系统时间

记录的日志的实际为utc时间，不适合查看，修改为system时间。

mysql> show global variables like 'log_timestamps';
+----------------+-------+
| Variable_name  | Value |
+----------------+-------+
| log_timestamps | UTC   |
+----------------+-------+

mysql> set global log_timestamps=SYSTEM;

mysql> show global variables like 'log_timestamps';
+----------------+--------+
| Variable_name  | Value  |
+----------------+--------+
| log_timestamps | SYSTEM |
+----------------+--------+