Try to replace subprocesses with DRb similar to Rails

[ilyazub]

Rails uses DRb when tests are parallelized with processes. Ref.

Try to replace Open3.popen3 with DRb and share results here. Probably it'll require a complete rewrite but there's not that much code.

I'm most interested in comparing file-based IPC & JSON-formatted messages with what DRb provides.