Suppress file output for the gltestthreading config

Bug: skia:
Change-Id: Icd905ea7e60a05bc3903eb85d111dcf73ce2c4dd
Reviewed-on: https://skia-review.googlesource.com/40690
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
2 files changed