Investigate flaky test test-cluster-worker-forced-exit

[joaocgreis]

Examples of failures:

• armv7-wheezy

[Trott]

Running this test 9999 times on armv7-wheezy results in no failures:
https://ci.nodejs.org/job/node-stress-single-test/28/nodes=armv7-wheezy/console

I propose removing its flaky designation in #3975

If/when it fails again, we can always add it back.

Otherwise, maybe something changed in the code or in CI that fixed the issue?

[rvagg]

we did do an upgrade of the slaves on armv7-wheezy at some point, probably between the OP and now, +1 to removing flaky, can you take care of that @Trott?

[Trott]

@rvagg: Yup. #3975