Interact with the docker API directly with curl or other HTTP tools.

For the JSON results, use jq to format

curl --unix-socket /var/run/docker.sock -H "Content-Type: application/json" http://localhost/version | jq

Rather than mocking all of docker, the tests require a functioning
docker system.  If you have docker running on /var/run/docker.sock,
set ALL_TESTING to 1 to run the tests, otherwise most tests are
skipped.

Some tests may get incorrect results if run in parallel or while other
Docker activities are occuring, Some may leave behind images or other
artifacts (though I'm trying to clean up after successful tests).
