subtests.docker_cli: Add detach and interaction test

This pull request implements the https://github.com/autotest/autotest-docker/pull/192 inside the test instead of framework to give it time to stabilize before turning it into framework. I believe that this implementation is cleaner and easier to follow than hybrid implementation from https://github.com/autotest/autotest-docker/pull/194

Kind regards,
Lukáš
I always prefer fail-safe. People are asked to close the socket/session/..., but sometimes you miss one branch where it not cleaned properly. For this there is default `__del__`. And as `close` can be executed multiple times, I don't see any problems with that.