Deprecate Windows support

Because WinStackers project has been retired, running OpenStack on
Windows operating systems is no longer maintained.

Change-Id: If4ad14a9f7f974c120c6d70c826a1bba358052a3

oslo_concurrency/processutils.py

@@ -26,6 +26,7 @@ import shlex
 import signal
 import sys
 import time
+import warnings
 
 import enum
 from oslo_utils import encodeutils
@@ -36,6 +37,11 @@ from oslo_utils import timeutils
 from oslo_concurrency._i18n import _
 
 
+if os.name == 'nt':
+    warnings.warn('Support for Windows OS is deprecated.',
+                  category=DeprecationWarning, stacklevel=3)
+
+
 # NOTE(bnemec): eventlet doesn't monkey patch subprocess, so we need to
 # determine the proper subprocess module to use ourselves.  I'm using the
 # time module as the check because that's a monkey patched module we use

releasenotes/notes/deprecate-windows-support-fcb77dddf82de36b.yaml

@@ -0,0 +1,4 @@
+---
+deprecations:
+  - |
+    Support for Windows operating systems has been deprecated.