test: fix flaky interval test

[apapirovski]

A test was recently introduced that consistently fails on OS X & a few other machines. This PR reliably fixes it.

CI: https://ci.nodejs.org/job/node-test-pull-request/12522/
Stress test CI: https://ci.nodejs.org/job/node-stress-single-test/1686/

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• tests and/or benchmarks are included
• documentation is changed or added
• commit message follows commit guidelines

Affected core subsystem(s)

test

[Trott]

LGTM. This version of the test fails on 9.3.0 and passes on master, which is exactly what we'd expect.

[Trott]

+1 to fast-tracking to unbreak CI

[apapirovski]

Thanks everyone. Landed in 8d04323

[Trott]

Alas, still flaky. https://ci.nodejs.org/job/node-test-commit-linux-containered/1416/nodes=ubuntu1604_sharedlibs_debug_x64/console

03:37:24 not ok 2014 sequential/test-timers-set-interval-excludes-callback-duration
03:37:24   ---
03:37:24   duration_ms: 1.220
03:37:24   severity: fail
03:37:24   stack: |-
03:37:24     assert.js:45
03:37:24       throw new errors.AssertionError(obj);
03:37:24       ^
03:37:24     
03:37:24     AssertionError [ERR_ASSERTION]: false == true
03:37:24         at Timeout.setInterval [as _onTimeout] (/home/iojs/build/workspace/node-test-commit-linux-containered/nodes/ubuntu1604_sharedlibs_debug_x64/test/sequential/test-timers-set-interval-excludes-callback-duration.js:14:5)
03:37:24         at ontimeout (timers.js:455:11)
03:37:24         at tryOnTimeout (timers.js:304:5)
03:37:24         at Timer.listOnTimeout (timers.js:267:5)
03:37:24   ...