WikibaseMediaInfo fails a tests when run under PHPUnit 6. Some database id is offThe suite attempts to insert a page with `page_id=2` but there is already a page with that id which causes a `1062 Duplicate entry '2' for key 'PRIMARY'`.
```
There was 1 error:
1) Wikibase\MediaInfo\Tests\MediaWiki\Maintenance\CreatePagePropsTest::testDBUpdates with data set #0 (array(array(2, 6, 'File.jpg', '', 0, 1, 0, '20180625104925', '20180625104925', 0, 213, 'wikitext', null), array(3, 6, 'File2.jpg', '', 0, 1, 0, '20180625104925', '20180625104925', 0, 213, 'wikitext', null)), array())
Wikimedia\Rdbms\DBQueryError: A database query error has occurred. with data set #0 (
array(
array(2, 6, 'File.jpg', '', 0, 1, 0, '20180625104925', '20180625104925', 0, 213, 'wikitext', null),
array(3, 6, 'File2.jpg', '', 0, 1, 0, '20180625104925', '20180625104925', 0, 213, 'wikitext', Did you forget to run your application's database schema updater after upgrading?null)
),
array())
Wikimedia\Rdbms\DBQueryError:
Query: INSERT INTO `unittest_page` (page_id,page_namespace,page_title,page_restrictions,page_is_redirect,page_is_new,page_random,page_touched,page_links_updated,page_latest,page_len,page_content_model,page_lang) VALUES ('2','6','File.jpg','','0','1','0','20180625104925','20180625104925','0','213','wikitext',NULL),('3','6','File2.jpg','','0','1','0','20180625104925','20180625104925','0','213','wikitext',NULL)
INSERT INTO `unittest_page`
(page_id,page_namespace,page_title,page_restrictions,page_is_redirect,page_is_new,page_random,page_touched,page_links_updated,page_latest,page_len,page_content_model,page_lang)
VALUES
('2','6','File.jpg','','0','1','0','20180625104925','20180625104925','0','213','wikitext',NULL),
('3','6','File2.jpg','','0','1','0','20180625104925','20180625104925','0','213','wikitext',NULL)
Function: Wikimedia\Rdbms\Database::insert
Error: 1062 Duplicate entry '2' for key 'PRIMARY' (localhost:/tmp/quibble-mysql-821zo5jf/socket)
/workspace/src/includes/libs/rdbms/database/Database.php:1443
/workspace/src/includes/libs/rdbms/database/Database.php:1413
/workspace/src/includes/libs/rdbms/database/Database.php:1186
/workspace/src/includes/libs/rdbms/database/Database.php:2010
/workspace/src/extensions/WikibaseMediaInfo/tests/phpunit/mediawiki/Maintenance/CreatePagePropsTest.php:114
/workspace/src/tests/phpunit/MediaWikiTestCase.php:469
/workspace/src/maintenance/doMaintenance.php:94
```
Repro: `check experimental` on dummy change: https://gerrit.wikimedia.org/r/#/c/mediawiki/extensions/WikibaseMediaInfo/+/441778/