http_pipe.py: replaced epoll with select to support Windows

Removed Unix-specific functionality in order to support Windows:
- select.epoll replaced with select.select
- SocketServer.ForkingMixIn replaced with SocketServer.ForkingMixIn
- socket.MSG_DONTWAIT replaced with socket.setblocking(False)

Even though epoll has a better performance and improved socket handling
than select, this change should not affect the actual test case.