test: investigate `parallel/test-npm-install` timeout

[refack]

• Version: master
• Platform: pi3-raspbian-jessie
• Subsystem: test,npm

128			parallel/test-npm-install	
duration_ms	120.86
severity		fail
stack		timeout

https://ci.nodejs.org/job/node-test-binary-arm/8953/RUN_SUBSET=3,label=pi3-raspbian-jessie/tapResults/
/cc @nodejs/npm @nodejs/build @nodejs/platform-arm

[tniessen]

Just in case you need this: https://ci.nodejs.org/job/node-test-binary-arm/8984/RUN_SUBSET=3,label=pi3-raspbian-jessie/console

not ok 128 parallel/test-npm-install
 ---
 duration_ms: 120.129
 severity: fail
 stack: |-
 timeout

[EDITED by trott to include console snippet because the CI link will be a 404 in a week or two.]

[refack]

FLAKY mark landed, and for the last few hours it's not failing, but still need a permanent solution

[Trott]

Closing in favor of earlier duplicate #13498. Re-open if I'm mistaken, of course.