Investigate flaky parallel/test-child-process-send-returns-boolean

[Trott]

• Version: 10.0.0-pre (master)
• Platform: macOS
• Subsystem: test child_process

https://ci.nodejs.org/job/node-test-commit-osx/17913/nodes=osx1010/console

not ok 593 parallel/test-child-process-send-returns-boolean
  ---
  duration_ms: 120.81
  severity: fail
  exitcode: -15
  stack: |-
    timeout

[Trott]

Reproduced easily on my laptop:

$ tools/test.py -j 96 --repeat 192 test/parallel/test-child-process-send-returns-boolean.js 
=== release test-child-process-send-returns-boolean ===                    
Path: parallel/test-child-process-send-returns-boolean
Command: out/Release/node /Users/trott/io.js/test/parallel/test-child-process-send-returns-boolean.js
--- TIMEOUT ---
=== release test-child-process-send-returns-boolean ===                   
Path: parallel/test-child-process-send-returns-boolean
Command: out/Release/node /Users/trott/io.js/test/parallel/test-child-process-send-returns-boolean.js
--- TIMEOUT ---
[02:07|% 100|+ 190|-   2]: Done  
$

[Trott]

(The timeout also has the unfortunate side effect of leaving a child process running.)

[Trott]

Proposed fix in #20136