Add tests for last-activity updates

[minrk]

tests for #292 - both that the usual activity is unchanged for simple successful requests, and that activity is not updated for failed requests

[consideRatio]

Node 10 LTS will reach end of life 2021-04-30, perhaps our next release should just stop supporting Node 10?

EDIT: https://nodejs.org/en/about/releases/

[minrk]

I think I'd rather use Ubuntu LTS as baseline supported node, given how little we need from it, unless there's a big reason to cut people off. 16.04 reaches end-of-maintenance this April, at which point 18.04 will be the oldest LTS release, which ships with node 8.