Use get_rpc_transport instead of get_transport
Use get_rpc_transport instead of get_transport

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/

Related-Bug: #1680192
Change-Id: I6b2ee043048bc380c4dd75638817f8152617ce09

openstack/manila,openstack/manila,bswartz/manila,bswartz/manila