Update nodejs for testharness to at least 8.4 to support newer http2 APIs

[mayhemer]

http2.createSecureServer API is needed for test for moz bug 1545421 - Propagate useful proxy errors to WebExtensions, important prerequisite for upcoming secure proxy.

Test introduced in that bug fails on infra with an exception when requiring 'http2'.

Notejs support originally introduced at 1313099 - Try pulling node from tooltool.

[valenting]

I'm not sure if it's relevant, but I also filed bug 1543624 a while ago.

[mayhemer]

Thanks for referencing it. Looks like we face the same issue. Let's see how this evolves.

[mayhemer]

We are still seeing errors on try. This needs to be reopened or explained what happened, why this has been prematurely closed - @garbas ?

[garbas]

@mayhemer sorry that was my mistake, i was on a issue closing spree since many of the issues here are not relevant anymore.