Unable to set kafka.metrics.reporter via environment variables in docker image

When passing broker configurations to the docker image, configurations have to be renamed as per https://github.com/apache/kafka/tree/trunk/docker/examples#using-environment-variables.

However there is an issue with kafka.metrics.reporters. It should be renamed to KAFKA_KAFKA_METRICS_REPORTERS but the logic converting it back to the configuration name strip all the KAFKA_ instances so we end up with only metrics.reporters which is not a valid configuration.