Track fiber tests (#7812)

Use the newly added tracking system to track the number of fiber tests that are passing/failing.

I first tried to modify the grunt lint rule for it and send the output in stdout but unfortunately grunt displays the rule + done messages there. I had like 30 lines of js already and I figured I could just write 3 lines of bash and it would work the same. Let me know if you want me to use another approach for it.

Test Plan:
Run the commands that have been introduced in this commit but the facts-tracker one
Run `echo $FIBER_TESTS` and make sure it prints `666/1434`