[3.6] bpo-30523, bpo-30764, bpo-30776: Sync regrtest from master (#2441)

* bpo-30523: regrtest --list-cases --match (#2401)

* regrtest --list-cases now supports --match and --match-file options.
  Example: ./python -m test --list-cases -m FileTests test_os
* --list-cases now also sets support.verbose to False to prevent
  messages to stdout when loading test modules.
* Add support._match_test() private function.
(cherry picked from commit ace56d583664f855d89d1219ece7c21c2fddcf30)

* bpo-30764: regrtest: add --fail-env-changed option (#2402)

* bpo-30764: regrtest: change exit code on failure

* Exit code 2 if failed tests ("bad")
* Exit code 3 if interrupted

* bpo-30764: regrtest: add --fail-env-changed option

If the option is set, mark a test as failed if it alters the
environment, for example if it creates a file without removing it.

(cherry picked from commit 63f54c68936d648c70ca411661e4208329edcf26)

* bpo-30776: reduce regrtest -R false positives (#2422)

* Change the regrtest --huntrleaks checker to decide if a test file
  leaks or not. Require that each run leaks at least 1 reference.
* Warmup runs are now completely ignored: ignored in the checker test
  and not used anymore to compute the sum.
* Add an unit test for a reference leak.

Example of reference differences previously considered a failure
(leak) and now considered as success (success, no leak):

    [3, 0, 0]
    [0, 1, 0]
    [8, -8, 1]
(cherry picked from commit 48b5c422ffb03affb00c184b9a99e5537be92732)

1 files changed, 18 insertions, 14 deletions

diff --git a/Lib/test/support/__init__.py b/Lib/test/support/__init__.py
index be926ea..677743b 100644
--- a/Lib/test/support/__init__.py
+++ b/Lib/test/support/__init__.py
@@ -1898,6 +1898,23 @@ def _run_suite(suite):
         raise TestFailed(err)
 
 
+def _match_test(test):
+    global match_tests
+
+    if match_tests is None:
+        return True
+    test_id = test.id()
+
+    for match_test in match_tests:
+        if fnmatch.fnmatchcase(test_id, match_test):
+            return True
+
+        for name in test_id.split("."):
+            if fnmatch.fnmatchcase(name, match_test):
+                return True
+    return False
+
+
 def run_unittest(*classes):
     """Run tests from unittest.TestCase-derived classes."""
     valid_types = (unittest.TestSuite, unittest.TestCase)
@@ -1912,20 +1929,7 @@ def run_unittest(*classes):
             suite.addTest(cls)
         else:
             suite.addTest(unittest.makeSuite(cls))
-    def case_pred(test):
-        if match_tests is None:
-            return True
-        test_id = test.id()
-
-        for match_test in match_tests:
-            if fnmatch.fnmatchcase(test_id, match_test):
-                return True
-
-            for name in test_id.split("."):
-                if fnmatch.fnmatchcase(name, match_test):
-                    return True
-        return False
-    _filter_suite(suite, case_pred)
+    _filter_suite(suite, _match_test)
     _run_suite(suite)
 
 #=======================================================================