* Store parsed docker-py / docker API versions in client.
* Began refactoring 'minimal required version' for docker_container options.
* Removing some fake defaults.
* Added changelog.
* Improve tests (check older docker versions).
* Fix comparison. The breaking point is not docker-py 2.0.0, but 1.10.0.
(Verified by testing with these versions.)
* Move docker-py/API version detection to setup_docker.
* Add YAML document starter.
* docker_network requirement for docker-py was bumped to 1.10.0 in #47492.
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