subtests.docker_cli: Add run_env test

This test contains workaround using InteractiveAsyncDockerCmd due of https://bugzilla.redhat.com/show_bug.cgi?id=1131592 and it fixes the issue https://github.com/autotest/autotest-docker/issues/252

this tests the ENV related features. Currently it only contains one
subsubtest, which is focused on linked containers. It sends data
using the addr from ENV to the server, which resends them back.

In the end it checks the valid data + ENV variables added via `-e x=y`
including the linked values ($linked_ENV_...)

Signed-off-by: Lukáš Doktor <ldoktor@redhat.com>
PS: Yes, there are solution, which might work, but they'd be slow and complicated (eg. you could check the status by `docker ps`, but then you need name or id, which means you need to modify every test which doesn't store them. It'd be duable with the proposed DockerManager, which creates containers and allows some hooks inside, but not generically).