* bpo-36670: regrtest bug fixes (GH-16537)

* Fix TestWorkerProcess.__repr__(): start_time is only valid
  if _popen is not None.
* Fix _kill(): don't set _killed to True if _popen is None.
* _run_process(): only set _killed to False after calling
  run_test_in_subprocess().

(cherry picked from commit 2ea71a07d0a720707094ee55f78fd232c40724bc)

* [3.8] Update libregrtest from master (GH-19516)

* bpo-37531: regrtest now catchs ProcessLookupError (GH-16827)

Fix a warning on a race condition on TestWorkerProcess.kill(): ignore
silently ProcessLookupError rather than logging an useless warning.

(cherry picked from commit a661392f8fb5ac4fc095aa1845d1eb7a25c4e9be)

* bpo-38502: regrtest uses process groups if available (GH-16829)

test.regrtest now uses process groups in the multiprocessing mode
(-jN command line option) if process groups are available: if
os.setsid() and os.killpg() functions are available.

(cherry picked from commit ecb035cd14c11521276343397151929a94018a22)

* bpo-37957: Allow regrtest to receive a file with test (and subtests) to ignore (GH-16989)

When building Python in some uncommon platforms there are some known tests that will fail. Right now, the test suite has the ability to ignore entire tests using the -x option and to receive a filter file using the --matchfile filter. The problem with the --matchfile option is that it receives a file with patterns to accept and when you want to ignore a couple of tests and subtests, is too cumbersome to lists ALL tests that are not the ones that you want to accept and he problem with -x is that is not easy to ignore just a subtests that fail and the whole test needs to be ignored.

For these reasons, add a new option to allow to ignore a list of test and subtests for these situations.

(cherry picked from commit e0cd8aa70a3ce19c3d3712568940aa0cbd9aa97b)

* regrtest: log timeout at startup (GH-19514)

Reduce also worker timeout.

(cherry picked from commit 4cf65a630a8d45bad3fe5cdc4c2632ec64e7ba27)

Co-authored-by: Pablo Galindo <Pablogsal@gmail.com>
(cherry picked from commit 67b8a1f0f0f78ec38b8626fa9f5b2f5a55c17e15)

* bpo-36842: Fix reference leak in tests by running out-of-proc (GH-13556)

(cherry picked from commit 9ddc416e9f6635376312c3615193f19480ac772a)

* Backport libregrtest changes from master

Co-authored-by: Steve Dower <steve.dower@python.org>