subtests.docker_cli: Add new test run_volumes_selinux

This test uses `docker run --volume ::Z/z` and checks it sets the
selinux context properly.

Signed-off-by: Lukáš Doktor <ldoktor@redhat.com>
I never needed to install this, but it's selinux-related module. So if you use `SUSE` I'm pretty sure it won't be installed and I want to be sure to generate `DockerTestNAError` Instead of `ImportError` which might require deeper analysis.