Goal: 

As a developer, I want run all the nova proxies to run with native threading, so that nova will work post Eventlet.

The proxies are:

• nova-novncproxy: handled separately in OSPRH-16766
• nova-serialproxy
• nova-spicehtml5proxy

Acceptance Criteria:

• proxies work in threading mode
• proxies work in Eventlet mode
• proxies uses the proper oslo.service backend based on the mode
• at least one upstream CI job exists that runs tempest with the proxies using threading mode
• proxies scale similarly in threading mode as in eventlet mode from both cpu and memory consumption perspective.
• as a special acceptance criteria here I want to only close this ticket when the upstream patches are landed and the nova-next job is running at least some of the proxies in threading mode to all incoming patches.

Note

If during the transformation we hit a scaling issue due the proxy runs one thread per connection and threads are more memory intensive than greenlets we might choose to investigate possible asyncio transformation of the proxies