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/monitor.py

@@ -53,7 +53,12 @@ class Monitor:
     def __del__(self):
         """Destruct the monitor object."""
         # We close the pubsub client to avoid leaking file descriptors.
-        self.primary_subscribe_client.close()
+        try:
+            primary_subscribe_client = self.primary_subscribe_client
+        except AttributeError:
+            primary_subscribe_client = None
+        if primary_subscribe_client is not None:
+            primary_subscribe_client.close()
 
     def subscribe(self, channel):
         """Subscribe to the given channel on the primary Redis shard.