Force reopening eventlet's hub after fork

With this we reopen eventlet's hub after a fork (triggered from
websockify when a new client connects) to prevent sharing epoll's fd
with the parent, which may cause erratic behaviour.

This caused novncproxy to stop working when it had more than two clients
connected.

Fixes bug #1193031

Change-Id: I3ff9001543b84b1037597da243422490bb611657
(cherry picked from commit cb25bc4)

nova/console/websocketproxy.py

@@ -42,6 +42,11 @@ def new_client(self):
         """
         Called after a new WebSocket connection has been established.
         """
+        # Reopen the eventlet hub to make sure we don't share an epoll
+        # fd with parent and/or siblings, which would be bad
+        from eventlet import hubs
+        hubs.use_hub()
+
         cookie = Cookie.SimpleCookie()
         cookie.load(self.headers.getheader('cookie'))
         token = cookie['token'].value