tests: fix test failures with node v19 change to default http clients to use keep-alive

[trentm]

As of nodejs/node#37184 node v19 and later
defaults the http,https.globalAgent to use keep-alive:

- globalAgent: new Agent()
+ globalAgent: new Agent({ keepAlive: true, scheduling: 'lifo', timeout: 5000 })

This change in default broke a couple tests. The agent itself is
unaffected because our http client already uses a custom http agent
using keep-alive.

---

This should fix recent Jenkins CI failures in the "Nightly Test" stage.
E.g. https://apm-ci.elastic.co/blue/organizations/jenkins/apm-agent-nodejs%2Fapm-agent-nodejs-mbp/detail/main/267/pipeline/7010

This started failing with the v19.0.0-nightly20220630350a6a8d59 nightly node build which included these node commits:

* 350a6a8d59 - perf_hooks: add initiatorType getter
* a0440c9174 - doc: add `backport-open-vN.x` step to backporting guide
* dc3e5408aa - tools: update lint-md-dependencies
* 49a5e81887 - src: fix compiler warning in src/heap_utils.cc
* ed1e9ae402 - events: improve `EventListener` validation
* 4267b92604 - http: use Keep-Alive by default in global agents
* 8e19dab677 - net: fix net keepalive and noDelay
* e2225ba8e1 - test_runner: expose `describe` and `it`
* d636fee319 - benchmark: fix fork detection

It is commit 4267b92604 - http: use Keep-Alive by default in global agents that was impacted our tests.

[trentm]

@astorm, I know you are off today. To get tests unblocked (there are currently 3 different issues in various test stages :) I will probably go ahead and merge this today once tests pass.

[apmmachine]

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• Start Time: 2022-07-04T20:06:19.221+0000

• Duration: 21 min 55 sec

Test stats 🧪

Test	Results
Failed	0
Passed	23803
Skipped	0
Total	23803

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[trentm]

Nightly tests passed now: https://apm-ci.elastic.co/blue/organizations/jenkins/apm-agent-nodejs%2Fapm-agent-nodejs-mbp/detail/PR-2803/2/pipeline