Fix Empty exception for timeout in send_request
Fix Empty exception for timeout in send_request

If the timeout parameter is set when making a request, for example when working with non-confirmable requests, the Empty exception may be raised and needs to be handled.

Traceback (most recent call last):
  File "nonclient.py", line 202, in <module>
    main()
  File "nonclient.py", line 139, in main
    response = client.send_request(req, None, 5)
  File "/root/CoAPthon/coapthon/client/helperclient.py", line 206, in send_request
    response = self.queue.get(block=True, timeout=timeout)
  File "/usr/lib/python2.7/multiprocessing/queues.py", line 132, in get
    raise Empty
Queue.Empty
Gnomjolnir/CoAPthon,Tanganelli/CoAPthon,Tanganelli/CoAPthon,Gnomjolnir/CoAPthon