PtyTests.run_child() now calls os.waitpid() to read the exit status
of the child process to avoid creating zombie process and leaking
processes in the background.
(cherry picked from commit 4baca1b)

Add a post_test_cleanup() function which currently only calls
support.reap_children().
(cherry picked from commit e3510d7)

(cherry picked from commit 3ca9f50)

TestRandomNameSequence.test_process_awareness() now calls
os.waitpid() to avoid leaking a zombie process.
(cherry picked from commit 6c8c294)