bpo-40094: Add test.support.wait_process() (GH-19254)

Moreover, the following tests now check the child process exit code:

* test_os.PtyTests
* test_mailbox.test_lock_conflict()
* test_tempfile.test_process_awareness()
* test_uuid.testIssue8621()
* multiprocessing resource tracker tests
diff --git a/Lib/test/test_random.py b/Lib/test/test_random.py
index c147105..548af70 100644
--- a/Lib/test/test_random.py
+++ b/Lib/test/test_random.py
@@ -1103,8 +1103,7 @@
                 child_val = eval(f.read())
             self.assertNotEqual(val, child_val)
 
-            pid, status = os.waitpid(pid, 0)
-            self.assertEqual(status, 0)
+            support.wait_process(pid, exitcode=0)
 
 
 if __name__ == "__main__":