Handle Ctrl+C gracefully
Handle Ctrl+C gracefully

Basically, there are two things we need to do: exiting *gracefully*
without emitting backtraces, and exiting *promptly* without waiting
for tests currently in progress to finish (or even worse, tests that
haven't even started yet).
bbannier/gtest-parallel,google/gtest-parallel,kwiberg/gtest-parallel,ehlemur/gtest-parallel,pbos/gtest-parallel