Enable using Unix sockets to communicate with containers

[aFuerst]

• Create Unix socket server that runs inside containers.
• Abstract container communication from container creation.
• Each container now has a special host folder for its "stuff"
• Using socket has ~6x reduction (~2-3 ms => 0.5 ms) in E2E platform overhead

How it works:

• Worker passes a environment var to the container indicating the socket path it must open.
• That folder is mounted from host container folder to that path
• Worker listens on that to be created.
• Uses a 2-message system to invoke.
  • First is a SendMessage with the first a u64 Command::Invoke and the len in bytes of the str arguments
  • Then the arguments are sent and deserialized by the worker
• Same system of sending message metadata first used to return results

TODOs:

• Add details to benchmark CSVs
• Push GPU containers that use Unix
• p99 results of some sort

This change is pretty much done, but I found a related problem. The worker runs into a scaling issue (or something) at high levels of client calls. Such that when running ~40 clients with high frequency invocations, using the scaling part of load gen and the simple hello image, the worker seems to stop responding. Not related to this issue I think, as it happens to the old HTTP client too

[prateek-s]

ok!