subtests.docker_cli: Add test run_cidfile

Fixes: https://github.com/autotest/autotest-docker/issues/264

This test is focussed on correct handling of `docker run --cidfile`

Signed-off-by: Lukáš Doktor <ldoktor@redhat.com>
Tip: sub-subtests come ready-made with a ``tmpdir`` nested below the parent tempdir and guaranteed unique.  So it may be slightly faster/safer to use ``tempfile.NamedTemporaryFile()`` (or similar) to make the file-object (and name).  It's not a big deal here though, no need to change it.