Explicitly use asyncio protocol for websockets

The new default for txaio (dependency of autobahn) requires that you
specify how you want websocket connections to be managed (asyncio or
twisted) and raises an exception if you don't make a choice.

Change-Id: I40695b17916cdd1795778be654a427210192ee2f

zaqar/transport/websocket/protocol.py

@@ -21,6 +21,7 @@ from autobahn.asyncio import websocket
 from oslo_log import log as logging
 from oslo_utils import timeutils
 import pytz
+import txaio
 
 try:
     import asyncio
@@ -51,6 +52,7 @@ class MessagingProtocol(websocket.WebSocketServerProtocol):
     }
 
     def __init__(self, handler, proto_id, auth_strategy, loop):
+        txaio.use_asyncio()
         websocket.WebSocketServerProtocol.__init__(self)
         self._handler = handler
         self.proto_id = proto_id