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

[vstinner]

TextTestRunner of unittest.runner now uses time.perf_counter() rather
than time.time() to measure the execution time of a test.

Similar change in libregrtest, and in pprint and random internal
tests.

https://bugs.python.org/issue35513

[miss-islington]

Thanks @vstinner for the PR 🌮🎉.. I'm working now to backport this PR to: 3.7.
🐍🍒⛏🤖

[bedevere-bot]

GH-11188 is a backport of this pull request to the 3.7 branch.

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot x86-64 High Sierra 3.7 has failed when building commit 9ade4cb.

What do you need to do:

1. Don't panic.
2. Check the buildbot page in the devguide if you don't know what the buildbots are or how they work.
3. Go to the page of the buildbot that failed (https://buildbot.python.org/all/#builders/147/builds/546) and take a look at the build logs.
4. Check if the failure is related to this commit (9ade4cb) or if it is a false positive.
5. If the failure is related to this commit, please, reflect that on the issue and make a new Pull Request with a fix.

You can take a look at the buildbot page here:

https://buildbot.python.org/all/#builders/147/builds/546

Click to see traceback logs

Traceback (most recent call last):
  File "/Users/buildbot/buildarea/3.7.billenstein-sierra/build/Lib/test/test_asyncio/test_events.py", line 272, in test_run_until_complete
    self.assertTrue(0.08 <= t1-t0 <= 0.8, t1-t0)
AssertionError: False is not true : 1.2684909640000015

----------------------------------------------------------------------

Ran 2029 tests in 74.737s

FAILED (failures=1, skipped=35)


Traceback (most recent call last):
  File "/Users/buildbot/buildarea/3.7.billenstein-sierra/build/Lib/test/test_asyncio/test_events.py", line 595, in test_signal_handling_args
    self.assertEqual(caught, 1)
AssertionError: 0 != 1

----------------------------------------------------------------------

Ran 2029 tests in 69.698s

FAILED (failures=1, skipped=35)