test: fix flaky test-http-regr-gh-2928
Fix flaky test-http-regr-gh-2928 that has been failing on Raspberry Pi devices in CI.
Fixes: https://github.com/nodejs/node/issues/4830
/cc @indutny
Confirmed (on OS X, anyway) that the test still segmentation faults (as expected/designed) when run with Node 4.1.0 but succeeds with Node 4.1.1.