When running `update.php`, the schema changes on the `globalblocks` table are not applied. This is because the table exists on a virtual database domain and so the `DatabaseUpdater` previously did not support applying the updates.
However, the `DatabaseUpdater` now supports applying schema changes to virtual database domains. This means we can update the #globalblocking code to perform these updates.
This will help keep local wikis up-to-date with schema changes to prevent errors, as otherwise the user has to manually apply SQL patch files to perform updates. This also means that the beta wikis have schema updates applied automatically. Furthermore, running `update.php` would create a `globalblocks` table on each local wiki database and this ends up being confusing.
========Acceptance criteria
* [] Code in `GlobalBlockingSchemaHooks` performs schema updates for the `globalblocks` table on the correct virtual database domain.