subtests..stop: Buletproof and simplify the stop test

Signed-off-by: Lukáš Doktor <ldoktor@redhat.com>
subtests.docker_cli: Add the docker kill test

This test compounds of 6 subtests. See the details in test docstrings.
Please note that most of them are failing, the bugs are commented in
TODO notes and will be fixed in case of correct behavior.

Signed-off-by: Lukáš Doktor <ldoktor@redhat.com>
subtests.docker_cli.stop: Pep8/pylint fixes

Signed-off-by: Lukáš Doktor <ldoktor@redhat.com>
Merge pull request #36 from ldoktor/kill

subtests.docker_cli: Add the docker kill test