Make test_multiprocessing cleanup properly

Previously, when an error was encountered some processes would not be
stopped until atexit callbacks were run.  On Windows that was too late
to prevent a PermissionError when regrtest tried to remove the temp
directory it ran the tests in.

Lib/test/test_multiprocessing.py

@@ -2555,6 +2555,8 @@ def _afunc(x):
 def pool_in_process():
     pool = multiprocessing.Pool(processes=4)
     x = pool.map(_afunc, [1, 2, 3, 4, 5, 6, 7])
+    pool.close()
+    pool.join()
 
 class _file_like(object):
     def __init__(self, delegate):
@@ -2808,13 +2810,16 @@ def test_main(run=None):
 
     loadTestsFromTestCase = unittest.defaultTestLoader.loadTestsFromTestCase
     suite = unittest.TestSuite(loadTestsFromTestCase(tc) for tc in testcases)
+    try:
         run(suite)
-
+    finally:
         ThreadsMixin.pool.terminate()
         ProcessesMixin.pool.terminate()
         ManagerMixin.pool.terminate()
+        ManagerMixin.pool.join()
         ManagerMixin.manager.shutdown()
-
+        ThreadsMixin.pool.join()
+        ProcessesMixin.pool.join()
         del ProcessesMixin.pool, ThreadsMixin.pool, ManagerMixin.pool
 
 def main():