Nomad: Docker auth from docker config

[jbardin]

I know secrets management is forthcoming, but it would also be nice if nomad could get docker auth from the default docker config files.

The client could just attempt to call NewAuthConfigurationsFromDockerCfg.

I'm trying to get nomad to pull images from an AWS ECR, which requires obtaining a new auth password from the API every 12 hours. The CLI command aws ecr get-login returns a docker login command to be eval'ed in the shell, which in turn is written to ~/.docker/config.json.

[jaygorrell]

Why was this closed? ECR doesn't behave like a standard private registry as the referenced PRs deal with.