V2.0.12 Session variable group_concat_max_len

[alpes214]

Description:
Track variable group_concat_max_len
Automated tests are updated.

Manual testing:

mysql> select * from performance_schema.session_variables where variable_name like '%group_concat_%';
+----------------------+----------------+
| VARIABLE_NAME        | VARIABLE_VALUE |
+----------------------+----------------+
| group_concat_max_len | 1024           |
+----------------------+----------------+
1 row in set (0.00 sec)

mysql> set group_concat_max_len=4096;
Query OK, 0 rows affected (0.00 sec)

mysql> select * from performance_schema.session_variables where variable_name like '%group_concat_%';
+----------------------+----------------+
| VARIABLE_NAME        | VARIABLE_VALUE |
+----------------------+----------------+
| group_concat_max_len | 4096           |
+----------------------+----------------+
1 row in set (0.00 sec)

[renecannao]

Instead of having a hardcoded list of variables, can we generate the list at runtime from mysql_tracked_variables ?
We can also have a mixed approach: some hardcoded variables + all the variables in mysql_tracked_variables , or some hardcoded variables + all the variables in mysql_tracked_variables that are handled by SETTING_VARIABLE , or some other way.
End goal: we should not modify this regex every time we want to track a new variable

[renecannao]

This also needs to be ported to 2.1.0