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: I37ba0aba489d3b3b9d00000549fc67cd05f1d3a4