Download files from task container

[emanaev]

When pulling task results send only new data, generated by task, not the whole container image.

[emanaev]

Guys, that is crucial feature for rendering, so please.

[emanaev]

The rationale is that the customer will not be interested in the whole result container image, he will be obviously interested in the results of the run. Furthermore, often he needs only one or several files which paths he knows in advance. Neural network training and CGI rendering are just such case.

So it would be sufficient to implement docker cp analogue. The user shall be able to download the file from the image locally for stopped containers as a minimum. Consider both uploading and downloading files both for running and stopped containers.

[3Hren]

AFAIK @oopcode has a research over it with reasonable and positive results. You don't need to explain the rationale behind this issue - it's quite obvious. Will increase the priority, okay.