Monkey patch original current_thread _active

Monkey patch the original current_thread to use the up-to-date _active
global variable. This solution is based on that documented at:
eventlet/eventlet#592

Change-Id: Icb26c43a71accdb4658ad6087fb3226f9a1090c0
Story: 2007614

os_ken/lib/hub.py

@@ -44,11 +44,20 @@
     import traceback
 
     getcurrent = eventlet.getcurrent
-    patch = eventlet.monkey_patch
     sleep = eventlet.sleep
     listen = eventlet.listen
     connect = eventlet.connect
 
+    def patch(thread=True):
+        eventlet.monkey_patch(thread=thread)
+        if thread:
+            # Monkey patch the original current_thread to use the up-to-date _active
+            # global variable. See https://bugs.launchpad.net/bugs/1863021 and
+            # https://github.com/eventlet/eventlet/issues/592
+            import __original_module_threading as orig_threading  # noqa
+            import threading  # noqa
+            orig_threading.current_thread.__globals__['_active'] = threading._active
+
     def spawn(*args, **kwargs):
         raise_error = kwargs.pop('raise_error', False)