Path corrections for font and css support files

Do-over for my hopelessly botched PR944, per Critic feedback. Updated gentest.py, regenerated applicable tests, and verified them on local server.

In the process, I noticed that these broken tests were logging as pass with testharness.js (yet clearly failing per canvas-tests.js logging). I haven't had time to look into it, but I filed https://github.com/w3c/web-platform-tests/issues/1037 for tracking.