With the added get_rpc_transport() function in oslo.messaging [1]
and the recent version bump of oslo.messaging to 5.24.2, we can
safely replace get_transport() with get_rpc_transport() which is much
cleaner.
[1] https://review.openstack.org/#/c/454194/
Change-Id: If165c438625f35b1c1cec1f125d1376e0d0edca5