test: fix flaky `test-child-process-pass-fd`

Listen on random ports instead of using `common.PORT`.

Fixes: https://github.com/nodejs/node/issues/8209
PR-URL: https://github.com/nodejs/node/pull/8212


Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Yorkie Liu <yorkiefixer@gmail.com>