Fix lingering processes for Gatsby telemetry and Jest worker

[ehmicky]

In #1889, we moved the lingering processes from the buildbot to Netlify Build.
The logic is currently the same. However, it happens a few seconds earlier.

It turns out some lingering processes are short-lived and terminate within a few seconds. Those were previously not reported to users due to the small duration between the end of the build command and the lingering process logic, which allowed them to complete. Now that this duration is smaller, they are being reported.

Ideally, those processes should be reported to the user and terminated, as mentioned in https://github.com/netlify/buildbot/issues/984

However, in order to decrease the amount of surprise for users for this specific release, I would suggest not reporting any warnings for the time being, for the top two offenders:

• Gatsby telemetry: node_modules/gatsby-telemetry/lib/send.js
• Jest child processes still running: node_modules/jest-worker/build/workers/processChild.js
• Broccoli Babel plugin: broccoli-babel-transpiler (known bug from that plugin)

We can then fix each of those libraries separately.

[ehmicky]

Done