subtests.docker_cli: Add images --all test

Fixes issue https://github.com/autotest/autotest-docker/issues/245 Please note that I put unrelated small typo-fix 62eae5c to spare another pull request.

this test focuses on differences between `docker images` and
`docker images --all`. Additionally it checks the image history and
verifies the automatic cleanup of untagged unused images.

The second variant with background containers sometimes generates failures, I haven't noticed any pattern (IDs are not matching... removing all containers helps, though)

Signed-off-by: Lukáš Doktor <ldoktor@redhat.com>