Investigate flaky test test-http-client-abort.js

[santigimeno]

It has failed on one of the pi2-raspbian-wheezy bots: https://ci.nodejs.org/job/node-test-binary-arm/RUN_SUBSET=1,nodes=pi2-raspbian-wheezy/1608/. Output:

# TIMEOUT
# Server listening.
# Making client 0
# Making client 1
# Making client 2
# Making client 3
# Making client 4
# Making client 5
# Making client 6
# Making client 7
# Making client 8
# Making client 9
# Making client 10
# Making client 11
# Making client 12
# Making client 13
# Making client 14
# Making client 15
# Got connection
# Got connection
# Got connection
# Got connection
# Got connection
# Got connection
# Got connection
# Got connection
# Got connection
# Got connection
# Got connection
# Got connection
# Got connection
# Got connection
# Got connection
# Client response code 200
# Client response code 200
# Client response code 200
# Client response code 200
# Client response code 200
# Client response code 200
# Client response code 200
# Client response code 200
# Client response code 200
# Client response code 200
# Client response code 200
# Client response code 200
# Client response code 200
# Client response code 200
# Client response code 200

[Trott]

Another one: https://ci.nodejs.org/job/node-test-binary-arm/1659/RUN_SUBSET=3,nodes=pi2-raspbian-wheezy/tapTestReport/test.tap-54/

[Trott]

Proposed fix: #6124