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

test-child-process-pass-fd needs to launch many processes
simultaneously. On Fedora 24, this can result in EAGAIN "Resource
temporarily unavailable" errors. When this occurs, simply try to launch
a worker again.

PR-URL: https://github.com/nodejs/node/pull/17598
Fixes: https://github.com/nodejs/node/issues/17589


Reviewed-By: Santiago Gimeno <santiago.gimeno@gmail.com>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>