Investigate (flaky?) test-http-set-timeout-server on SmartOS

[Trott]

Example failure: https://ci.nodejs.org/job/node-test-commit-smartos/2074/nodes=smartos14-32/tapTestReport/test.tap-491/

not ok 491 test-http-set-timeout-server.js
# events.js:154
#       throw er; // Unhandled 'error' event
#       ^
# 
# Error: listen EADDRINUSE :::12346
#     at Object.exports._errnoException (util.js:893:11)
#     at exports._exceptionWithHostPort (util.js:916:20)
#     at Server._listen2 (net.js:1225:14)
#     at listen (net.js:1261:10)
#     at Server.listen (net.js:1358:5)
#     at serverResponseTimeoutWithPipeline (/home/iojs/build/workspace/node-test-commit-smartos/nodes/smartos14-32/test/parallel/test-http-set-timeout-server.js:128:10)
#     at run (/home/iojs/build/workspace/node-test-commit-smartos/nodes/smartos14-32/test/parallel/test-http-set-timeout-server.js:19:5)
#     at Server.<anonymous> (/home/iojs/build/workspace/node-test-commit-smartos/nodes/smartos14-32/test/parallel/test-http-set-timeout-server.js:105:5)
#     at emitOne (events.js:90:13)
#     at Server.emit (events.js:182:7)
# # serverTimeout
# # serverRequestTimeout
# # serverResponseTimeout
# # serverRequestNotTimeoutAfterEnd
# # serverResponseTimeoutWithPipeline
  ---
  duration_ms: 0.722

/cc @nodejs/testing

[santigimeno]

Proposed fix in: #6248