updater: Move rev_sha1 addition before convertUserOptions

Execution of the script and addition of rev_sha1 are both 1.19
activities, but for some reason the issue has only shown up in 1.21.

* MysqlUpdater::getCoreUpdateList() declares that 'doMigrateUserOptions'
  should be executed before adding the field rev_sha1 into the revision table
* ConvertUserOptions::execute() calls User::saveSettings()
* User::saveSettings() at its very end calls $this->getUserPage()->invalidateCache()
  and that is where the revision query is joining the party.

Bug: 48820
Change-Id: Id0a6efc33a8c46fdc3e9c294aa2d005d46c7dda0
(cherry picked from commit 070b8b40fb9cc2b4912f9c1b06d93712c0b2ddf3)