bpo-37421: multiprocessing tests now stop ForkServer (GH-14601)


multiprocessing tests now stop the ForkServer instance if it's
running: close the "alive" file descriptor to ask the server to stop
and then remove its UNIX address.
(cherry picked from commit 8fbeb14312b4c1320d31ad86e69749515879d1c3)

Co-authored-by: Victor Stinner <vstinner@redhat.com>
3 files changed