Use docker-py

[petrmvala]

This pull request first fixes some code style and then uses python module docker-py instead of calling docker commands in subprocess.

[petrmvala]

Hello Andrey, thank you for your comments. To be honest, I still consider this a work in progress, and posted it mainly for michalsustr to have a look at it. That being said, I value your input and consider it.

You shouldn't need to rebuild images, as this PR is about keeping functionality, but using docker-py instead of invoking docker commands through subprocess command.

[michalsustr]

I'm not sure that I have right to share my concerns, but let's raise them.

Sure, feedback is welcome! BTW, this is a WIP of one my friend who wanted to try to contribute to open source.

please give me a bit of time to check that docker-machine scenario is correctly supported.

Thanks! I will let you know.

I will add a few more:

• heavy use of non-intelligible variable names like "output"
• exception tracebacks can become lost, effectively reducing available bug information for issue tracker
• triple quotes should be used for docstrings """ instead of '''