subtests.docker_cli.kill: Add non-tty variant

This modification enables all docker_cli/kill subtests to run on
tty and nontty container. It's not perfect, but it does the job.

The main issue of this solution is, that config is printed during `__init__` and it's changed afterwards. Anyway I'm not convinced about this method and it's only in this test. If we want to put this into framework, we might want to support the substitution during `SubSubtest.__init__()` and print the correct configuration.

There is related issue with similar solution, currently `SubSubtest` prints name using `self.__class__.__name__`. When we create multi-variant subtests, the name should be different. That's why I put `Executing subsubtest %s variant %s` string before each variant to simplify searching for each variant.

Short note about the used multi-varianting, it's supports only flat variant definition. This suffice in this example, but in a future we might want to combine the variants. This would be hard using this way. Anyway I still haven't found any good way for this using current INI format. (yes, I miss cartesian a lot)

__Even on my laptop this test is hitting the 600s timeout. Correct me if I'm wrong, but with the current `control` file it's impossible to change this value for particular Subtest, right?__

Regards,
Lukáš