logs() separate param for stream and follow

[dnephin]

From: https://github.com/docker/compose/pull/2720/files#r52222296

Current the follow param is set based on stream

I think follow=True does imply stream=True, but stream=True doesn't imply follow=True, you may still want to stream without following.

[TomasTomecek]

This is about performance, right? (and I guess integrity, one can only have a single piece of code to handle streamed response)

[dnephin]

I don't think it's just about performance. It's to support follow=False, stream=True.

Stream is a client-side option, follow is a server side option. We want to be able to stream (read the http response line by line and return an iterator instead of buffering the entire response), and not follow the logs.

Otherwise running logs(stream=False) on a container with lots of logs would cause the process to use lots of memory (which I guess in a sense is performance related).