bpo-35513, unittest: TextTestRunner uses time.perf_counter() (GH-11180)

TextTestRunner of unittest.runner now uses time.perf_counter() rather
than time.time() to measure the execution time of a test: time.time()
can go backwards, whereas time.perf_counter() is monotonic.

Similar change made in libregrtest, pprint and random.
6 files changed