Replace `timeout_deferred` with `deferred.addTimeout`

Replace [`timeout_deferred`](https://github.com/rackerlabs/otter/blob/b4b858a186660e095bb6290bc48e659172cf41bd/otter/util/deferredutils.py#L62) with [`deferred.addTimeout`](http://twistedmatrix.com/documents/current/api/twisted.internet.defer.Deferred.html#addTimeout) introduced in Twisted 16.5.