This prints out a large gtest_filter of the tests in a batch. Makes
reproducing a particular failure much easier.

In the future we could potentially look at using an encoding to
reproduce a specific batch: e.g. a flag that acceps a batch / shard
number and runs those tests based on using the same internal counts.

Bug: angleproject:5172
Change-Id: Iefad8f5ca23761417ad1ceb11fd664c9cf23c8be
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2475455
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Courtney Goeltzenleuchter <courtneygo@google.com>
Reviewed-by: Yuly Novikov <ynovikov@chromium.org>