test: make test-process-argv-0 robust

Remove use of STDERR to avoid test flakiness on CentOS 5.

Use parent process exit event for assertion rather than child exit
event.

PR-URL: https://github.com/nodejs/node/pull/2541
Fixes: https://github.com/nodejs/node/issues/2477


Reviewed-By: Michaël Zasso <mic.besace@gmail.com>