We need to flesh out an upstream API to allow the NRM to be controlled from other software.

We have at least two clients of this API in mind:

• GRM/Flux: to send resource requests, and launch jobs
• a CLI client, to launch containers and other stuff interactively

There are several factors that make an pub/sub interface a good idea there:

• GRM wants to request changes in resources in an asynchronous, idempotent way. This is for scaling and coupling reasons. As such, GRM acts as a publisher, and the NRM as a subscriber.
• Flux will need to be interfaced by listening to events on the Flux bus, so Flux will be a publisher and NRM subscriber also.
• while the CLI client could follow a more typicall REQ/REP pattern, if we need to send back to the client the stdout/stderr from the container, we probably want to also have a publisher socket.
• This is also the case for Flux, that expects events to be published for stdout/stderr.
  Those constraints push us to have:
• a SUB socket to listen for commands
• a PUB socket to respond to those commands, forward data on current events

The TODO for this issue are:

• Add pub/sub sockets for this API
• Add callback to event loop to capture messages on those sockets
• Implement basic command manager, to keep track of non-completed commands
• Implement basic commands handling for:
  • run container
  • list container
  • kill container
  • send acks to API clients
  • send results to API clients
• Implement basic CLI binary to test the commands
• Merge draft power control API into this facility