* bpo-31234: Join threads in tests (#3572)

Call thread.join() on threads to prevent the "dangling threads"
warning.

(cherry picked from commit 18e95b41)

* bpo-31234: Join threads in test_hashlib (#3573)

* bpo-31234: Join threads in test_hashlib

Use thread.join() to wait until the parallel hash tasks complete
rather than using events. Calling thread.join() prevent "dangling
thread" warnings.

* test_hashlib: minor PEP 8 coding style fixes

(cherry picked from commit 8dcf22f4)

* bpo-31234: Join threads in test_threading (#3579)

Call thread.join() to prevent the "dangling thread" warning.

(cherry picked from commit b8c7be2c)

* bpo-31234: Join threads in test_queue (#3586)

Call thread.join() to prevent the "dangling thread" warning.

(cherry picked from commit 167cbde5)

* bpo-31234: Join timers in test_threading (#3598)

Call the .join() method of threading.Timer timers to prevent the
"threading_cleanup() failed to cleanup 1 threads" warning.

(cherry picked from commit da3e5cf9)