role:icinga2_master: Set new defaults for MariaDB

`table_definition_cache`:
* MariaDB default: 400
* Icinga comes with 540 tables
* Set default for Icinga to 550

`innodb_log_file_size`:
* `innodb_buffer_pool_size` default: `128M` (enough for a fresh Icinga installation)
* THerefore set the default for `innodb_log_file_size` to `32M` (25%)