flaky test

We have a test that fails occasionally:
$ make
python -m testtools.run discover
Tests running...
----------------------------------------
Exception happened during processing of request from ('127.0.0.1', 47554)
Traceback (most recent call last):
  File "/home/jameinel/dev/u1db/work/u1db/remote/sync_server.py", line 55, in process_request_thread
    self.finish_request(request, client_address)
  File "/usr/lib/python2.7/SocketServer.py", line 323, in finish_request
    self.RequestHandlerClass(request, client_address, self)
  File "/usr/lib/python2.7/SocketServer.py", line 639, in __init__
    self.handle()
  File "/home/jameinel/dev/u1db/work/u1db/tests/test_remote_sync_server.py", line 48, in handle
    value = self.request.recv(1024)
  File "/usr/lib/python2.7/socket.py", line 170, in _dummy
    raise error(EBADF, 'Bad file descriptor')
error: [Errno 9] Bad file descriptor
----------------------------------------

I'm pretty sure this is just shutdown code that is triggering, and the socket is already closed by the time we go to check for the next request, etc.

Really we should just handle EBADF and exit without reporting an error.