subtests.docker_cli: Add logs_follow test

This test uses `docker logs --follow` and checks it works correctly. (Issue https://github.com/autotest/autotest-docker/issues/250 )

Signed-off-by: Lukáš Doktor <ldoktor@redhat.com>
Well what it does is in the `Output` docstring, in the `pylint` line I describe why I disable things...