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'm not a python guru enough to substitute class with lambda. Anyway if you have working code which wraps anything and prints it on `__str__` call, please post it here and I'll gladly use it.