Internal shader cache caused timeout in some dEQP tests.
Work-around: ignore the cache by hooking fopen function and return null
when the cache related files are accessed.

Bug: angleproject:5354
Change-Id: I12ca228540925e67454bf24ce1ba83d703882c87
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2580918
Commit-Queue: Le Hoang Quyen <le.hoang.q@gmail.com>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Kenneth Russell <kbr@chromium.org>