Add variable Innodb_checkpoint_max_age

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mysql> show status like 'Innodb_checkpoint%';
+-----------------------+-------+
| Variable_name         | Value |
+-----------------------+-------+
| Innodb_checkpoint_age | 0     |
+-----------------------+-------+
1 row in set (0.00 sec)

mysql> show status like 'Innodb_checkpoint_max_age';
Empty set (0.00 sec)