QUICKFIX: Ignore `kevent:  Invalid Argument’ warnings
QUICKFIX: Ignore `kevent:  Invalid Argument’ warnings

Some users are seeing millions of lines of `[warn] kevent: Invalid argument` being produced while running headless chrome on Mac.

I have confirmed this on some large apps tests suites:

OS: MacOs 10.13.4 (17E202)
Chrome: Version 67.0.3396.62 (Official Build) (64-bit)

We should likely not buffer `stderr` or `stdout` in memory, I hope to circle back shortly. This commits aims to unblock


Opened a chrome issue: https://bugs.chromium.org/p/chromium/issues/detail?id=849818
Issue tracking a proper fix: https://github.com/testem/testem/issues/1265
testem/testem,testem/testem,testem/testem,johanneswuerbach/testem,johanneswuerbach/testem,johanneswuerbach/testem