WikiaLogger: add more context when logging from maintenance scripts

https://wikia-inc.atlassian.net/browse/PLATFORM-431

@Wikia/platform-team 

Add more context for log entries from maintenance scripts

```php
 '@fields' =>
  array(5) {
    'db_name' =>
    string(8) "plpoznan"
    'city_id' =>
    string(4) "5915"
    'maintenance_file' =>
    string(59) "/usr/wikia/source/app/maintenance/wikia/purgeWebPThumbs.php"
    'maintenance_class' =>
    string(15) "PurgeWebPThumbs"
    'request_id' =>
    string(25) "mw541850e3577f32.71699233"
  }

```