test,tracing: use close event to wait for stdio

Use `'close'` rather than `'exit'` to make sure that all stdio
has been captured by the time that the event handler is run.

PR-URL: https://github.com/nodejs/node/pull/25894


Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Anto Aravinth <anto.aravinth.cse@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>