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/spicehtml5proxy to stop working when it had more
than two clients connected.

Fixes bug #1193031

Change-Id: I3ff9001543b84b1037597da243422490bb611657
Merge "Force reopening eventlet's hub after fork" into stable/grizzly