Overwrite output lines for successful tests
Overwrite output lines for successful tests

This gives a tiny speed boost, since there's less scrolling, but more
importantly it means that interesting error messages from failing
tests won't scroll off the screen just because they're followed by
hundreds of tests that don't fail.

bbannier/gtest-parallel,kwiberg/gtest-parallel,pbos/gtest-parallel,google/gtest-parallel,ehlemur/gtest-parallel,greggomann/gtest-parallel