ModuleInstances should be executed as processes, not threads

[pbloem]

Also in the LocalExecutionProfile.

This would help us to create an environment where every module (in whatever domain) can just write to the current working directory, current in/out etc. and ducktape will catch it, and put it in the right place.

With any other solution (like threads) the modules must be written with techniques that are specific to ducktape, which is what we're trying to avoid.

The only problem is that this might increase the overhead, but probably not by that much.