* Check minimal API and docker-py versions for all docker_* tests.
* Improve docker_swarm creation/destruction for tests.
* Fail when conditions aren't met.
* Don't hardcode address for advertise_addr.
* Add docker_image_facts tests.
* Add basic integration test for docker_volume.
* Add basic docker_image tests.
* Only start test registry when tests are actually run (i.e. not on CentOS 6).
