'Query the devices for a user id hosted on a remote server.
Response:
"stream_id": "...",
"devices": [ { ... } ]
Args:
destination(str): The server to query.
query_content(dict): The user ids to query.
Returns:
A dict containg the device keys.'

@defer.inlineCallbacks
@log_function
def query_user_devices(self, destination, user_id, timeout):

    path = ((PREFIX + '/user/devices/') + user_id)
    content = (yield self.client.get_json(destination=destination, path=path, timeout=timeout))
    defer.returnValue(content)
