attempt to read ~/.docker/config.json for registry auths

[evandam]

Description

Rough attempt to resolve #261 by reading ~/.docker/config.json to get auths for an image's registry rather than relying on a single creds_file while not breaking any existing compatibility (by introducing a new docker_config_auth flag). I'm sure it's far from perfect, but hoping this is a good jumping off point and folks have better ideas.

I realize image_registry = image.split('/').first will often be misleading especially for official images on DockerHub, but might be good enough.

Looks like there's some similar work in https://github.com/test-kitchen/kitchen-dokken/pull/189/files but not sure 🤷‍♂️

Issues Resolved

Fixes #261

Check List

• All tests pass. See TESTING.md for details.
• New functionality includes testing.
• New functionality has been documented in the README if applicable.

[PJB3005]

This seems to break Kitchen if you don't have a ~/.docker/config.json (file not found error) and then a nil value call if you don't have an auths key in it.

[thenoid]

Aye this is breaking for us as well.

[evandam]

Hey folks, I opened a new PR that should address this #276