test: fix flaky test-http-set-timeout

[Trott]

Pull Request check-list

• Does make -j8 test (UNIX) or vcbuild test nosign (Windows) pass with
  this change (including linting)?
• Is the commit message formatted according to [CONTRIBUTING.md][0]?
• If this change fixes a bug (or a performance problem), is a regression
  test (or a benchmark) included?
• Is a documentation update included (if this change modifies
  existing APIs, or introduces new ones)?

Affected core subsystem(s)

test

Description of change

Increase timeout on Raspberry Pi to alleviate flakiness.

Fixes: #5854

[Trott]

Stress test that will hopefully show flakiness on master: https://ci.nodejs.org/job/node-stress-single-test/564/nodes=pi1-raspbian-wheezy/console

Stress test that will hopefully show no flakiness with this change: https://ci.nodejs.org/job/node-stress-single-test/565/nodes=pi1-raspbian-wheezy/console

(They've both been compiling for 2.5 hours...pi1 platform, whatcha gonna do, rite?)

[jasnell]

LGTM

[cjihrig]

LGTM

[Trott]

100 runs did not seem to be enough to get a flaky result on master. Trying 999.

master: https://ci.nodejs.org/job/node-stress-single-test/566/nodes=pi1-raspbian-wheezy/console

this branch: https://ci.nodejs.org/job/node-stress-single-test/567/nodes=pi1-raspbian-wheezy/console

[Trott]

Stress test at 999 jobs still does not reproduce issue on master, but we have the one example and this would seem to be an improvement, so...

CI: https://ci.nodejs.org/job/node-test-pull-request/2060/

[Trott]

Landed in 04ac1c0