* Improve error for docker modules when docker-py can't be imported.
* Add changelog.
* Mention platform and Python interpreter in more cases.
* Clarify wording.
* Adjust tests.
(cherry picked from commit 4a12be31fb)
* Improve error for docker modules when docker-py can't be imported.
* Add changelog.
* Mention platform and Python interpreter in more cases.
* Clarify wording.
* Adjust tests.
(cherry picked from commit 4a12be31fb)