test: skip http2 tests older Node.js

[lamweili]

Allows skipping of all http2 tests (for older Node.js) by scoping them in a describeHttp2('http2') block as part of PR pillarjs#34.

[tellnes]

Hi. I'm not actively maintaining my fork of https://github.com/pillarjs/finalhandler, so I did not see this. But might I ask why you need this change. What problem does it actually solve?

if the problem discussed in pillarjs#34 is a problem for you, I recommend you follow up in that issue or in Node.js core.

[lamweili]

It will skip the http2 tests on older Node.js that does not support http2. Currently, it return done() instead of skipping, which is a false positive. Skipping is more correct.

So this PR, if merged into http2-warning branch, will automatically update and improve your PR pillarjs#34.

[tellnes]

Ah, yes. That is better. I'll merge it in if this is going to be merged upstream. Then I need to rebase it also since it has a merge conflict now.

[lamweili]

Probably you should do the merge + rebase so the PR over there gets updated with more likelihood of getting merged. Otherwise I think the maintainers over there might overlook this PR.