Refactor volume proxy code out of the persona

[sflxn]

Refactor all the swagger code related to volumes in the persona daemon to their own proxies so that new clients of the portlayer can be created without needing to deal with swagger.

Acceptance Criteria:

• Volume swagger code refactored out of the persona's backend
• These proxies are moved from lib/apiservers/engine/backend to lib/apiservers/engine/proxy
• ops tracing added to the proxy code
• unit tests for the proxy code

[sflxn]

Unfortunately, the volume code must be refactored with the container and system proxies at the same time.