Fix incorrect transport property

The oslo.messaging library is expecting a property called transport_url
not transport_host. Because we are setting the notifier_strategy to
'default' without a valid transport oslo.messging does not know which MQ
driver to instantiate and it can instantiate Rabbit's even though the MQ
type might be QPID.

Change-Id: Ib29aee1ce06712c43a457dfe8c9a3efdce5a8f33
Closes-Bug: #1311823