Upgrade demo.moodle.net to 3.4

Thanks David, all looking fine now.

Just noting that I have installed two more new language packs - Igbo (ig) and Pidgin (pcm).

After fixing the problem with the reset script, the slave sites is now reset correctly. Thanks everybody.

Note: it did not work as expected, @Matthew Spurrier informed via telegram

The fix has been deployed to demomaster (https://demomaster.moodle.net/?theme=clean) and reset snapshot has been taken. Starting with the second next hourly reset (in 1 hour 20 minutes), it should be available on demo.moodle.net

This has been fixed on both branches demo.moodle.net-3.4-test and demo.moodle.net-3.4-deploy

I don't know the correct procedure to deploy these branches to the new system - may I ask @Matthew Spurrier or @Mark Paget for finishing this fix. Thanks guys.