oslo.messaging drivers should provide user management API

[Amrith Kumar]

Currently oslo.messaging provides no user management API's. It would be good if oslo.messaging allowed clients to perform user and ACL management operations.

In other words, messaging would expose API's that would cause the underlying transport (i.e. oslo messaging would send to the right driver) to create and delete users, grant users access to exchanges and so on.

This would allow clients of oslo.messaging (like Trove) to create and manipulate users and permissions directly without having to directly interact with the underlying transport.