regrtest: add a summary of the summary, "Result: xxx"

It's sometimes hard to check quickly if tests succeeded, failed or something
bad happened. I added a final "Result: xxx" line which summarizes all outputs
into a single line, written at the end (it should always be the last line of
the output).
diff --git a/Lib/test/libregrtest/main.py b/Lib/test/libregrtest/main.py
index 0723c43..78c52bd 100644
--- a/Lib/test/libregrtest/main.py
+++ b/Lib/test/libregrtest/main.py
@@ -431,6 +431,14 @@
         duration = time.monotonic() - self.start_time
         print("Total duration: %s" % format_duration(duration))
 
+        if self.bad:
+            result = "FAILURE"
+        elif self.interrupted:
+            result = "INTERRUPTED"
+        else:
+            result = "SUCCESS"
+        print("Result: %s" % result)
+
         if self.ns.runleaks:
             os.system("leaks %d" % os.getpid())
 
diff --git a/Lib/test/test_regrtest.py b/Lib/test/test_regrtest.py
index 0b6f2ea..40862e6 100644
--- a/Lib/test/test_regrtest.py
+++ b/Lib/test/test_regrtest.py
@@ -349,7 +349,7 @@
         return list(match.group(1) for match in parser)
 
     def check_executed_tests(self, output, tests, skipped=(), failed=(),
-                             omitted=(), randomize=False):
+                             omitted=(), randomize=False, interrupted=False):
         if isinstance(tests, str):
             tests = [tests]
         if isinstance(skipped, str):
@@ -398,6 +398,17 @@
                 regex = 'All %s' % regex
             self.check_line(output, regex)
 
+        if interrupted:
+            self.check_line(output, 'Test suite interrupted by signal SIGINT.')
+
+        if nfailed:
+            result = 'FAILURE'
+        elif interrupted:
+            result = 'INTERRUPTED'
+        else:
+            result = 'SUCCESS'
+        self.check_line(output, 'Result: %s' % result)
+
     def parse_random_seed(self, output):
         match = self.regex_search(r'Using random seed ([0-9]+)', output)
         randseed = int(match.group(1))
@@ -658,7 +669,8 @@
         code = TEST_INTERRUPTED
         test = self.create_test('sigint', code=code)
         output = self.run_tests(test, exitcode=1)
-        self.check_executed_tests(output, test, omitted=test)
+        self.check_executed_tests(output, test, omitted=test,
+                                  interrupted=True)
 
     def test_slowest(self):
         # test --slowest
@@ -681,10 +693,11 @@
             else:
                 args = ("--slowest", test)
             output = self.run_tests(*args, exitcode=1)
-            self.check_executed_tests(output, test, omitted=test)
+            self.check_executed_tests(output, test,
+                                      omitted=test, interrupted=True)
+
             regex = ('10 slowest tests:\n')
             self.check_line(output, regex)
-            self.check_line(output, 'Test suite interrupted by signal SIGINT.')
 
     def test_coverage(self):
         # test --coverage