test: make listen-fd-cluster/server more robust
- eliminate unnecessary intermediate process ("parent")
- children exit if runner dies unexpectedly (killed on a test timeout,
for example)
- use explicit messaging from children to parents to indicate when
worker is ready to accept http requests, rather than racing to see
whether runner will make request before worker is listening
PR-URL: https://github.com/nodejs/io.js/pull/1944
Reviewed-By: Johan Bergstrom <bugs@bergstroem.nu>
Reviewed-By: Ben Noordhuis <ben@strongloop.com>