[Features] Support upate parameters in non-default sections, e.g client or mysql

[sophon-zt]

e.g:

1. update rpl-semi-sync-master-enabled : --set rpl-semi-sync-master-enabled = ON OR --set mysqld.rpl-semi-sync-master-enabled = ON
2. update default-character-set: --set mysql.default-character-set = utf8mb4
3. update port : set client.port = 3306

[mysqld]
rpl-semi-sync-master-enabled = 1
rpl_semi_sync_master_timeout = 1000
rpl-semi-sync-slave-enabled = 1

[mysql]
default-character-set=utf8mb4

[client]
port=3306
socket=/var/run/mysqld/mysqld.sock
default-character-set=utf8mb4