HTTP integration tests are too flaky

[dyladan]

The http instrumentation tests are so flaky at this point that I am seeing failures on at least one of the node versions for almost every PR. The instrumentation tests currently reach out to the real internet and test a variety of features already covered by unit tests. I think we should drastically simplify any http testing which requires async requests to just a single representative example which uses the most common features. Other things are, or should be, sufficiently covered by unit tests.

[vmarchaud]

not sure why the tests are specially flaky with the instrumentation (instead of the plugin).

I'm not sure why we have integration tests (either with 3rd parties modules or that reach internet), i don't see any benefits since unit test covers both the server and client quite fine. Plus testing 3rd party modules that use the core http module anyway seems redundant.

[dyladan]

Fixed in #1808