test: refactor test-http-pipeline-flood

This extends fixes for test-https-pipeline-flood to hopefully fully
eliminate its flakiness on Windows in our continuous integration
process.

PR-URL: nodejs#3636
Reviewed-By: Ben Noordhuis <[email protected]>

Author: Trott

test/sequential/sequential.status

@@ -7,7 +7,6 @@ prefix sequential
 [true] # This section applies to all platforms
 
 [$system==win32]
-test-http-pipeline-flood                        : PASS,FLAKY
 
 [$system==linux]
 test-vm-syntax-error-stderr                     : PASS,FLAKY