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
It's not a fail-safe, it's a hidden fail-dangerous.  You're assuming ``self.close`` is never overridden and the parent class never adds it's own ``__del__``.  Worse, you have no control over when ``__del__`` is called, it happens on garbage-collection, not out-of-scope or ``del`` time.  It's always better to have explicit behaviour, unless there's a really really really good reason not to.  Calling another method is not a good enough reason for me to introduce possibly all kinds of hidden behaviors.