Make more tests run on Windows (#8446)

* Remove worker Wait() call due to SIGCHLD being ignored

* Port _pid_alive to Windows

* Show PID as well as TID in glog

* Update TensorFlow version for Python 3.8 on Windows

* Handle missing Pillow on Windows

* Work around dm-tree PermissionError on Windows

* Fix some lint errors on Windows with Python 3.8

* Simplify torch requirements

* Quiet git clean

* Handle finalizer issues

* Exit with the signal number

* Get rid of wget

* Fix some Windows compatibility issues with tests

Co-authored-by: Mehrdad <noreply@github.com>

python/ray/tests/test_component_failures.py

@@ -1,5 +1,5 @@
 import os
-from signal import SIGKILL
+import signal
 import sys
 import time
 
@@ -8,6 +8,8 @@ import pytest
 import ray
 from ray.test_utils import run_string_as_driver_nonblocking, SignalActor
 
+SIGKILL = signal.SIGKILL if sys.platform != "win32" else signal.SIGTERM
+
 
 # This test checks that when a worker dies in the middle of a get, the plasma
 # store and raylet will not die.