Plugin doesn't correctly bubble up Docker Hub Rate Limiting Error

[HugeIRL]

If you get rate limited from Docker Hub: https://www.docker.com/increase-rate-limits/

The error you get from the plugin is a bit misleading: Error response from daemon: pull access denied for api, repository does not exist or may require 'docker login': denied: requested access to the resource is denied

We should actually either bubble up the rate limit error (if it exists), or be more specific on the error so folks know it might be a rate limiting issue. If you don't know that you're being rate limited from Docker, this error isn't as clear as it could be.