Update accumulo-proxy Docker container to be more size efficient

During the pull request here: https://github.com/apache/accumulo-proxy/pull/20 @mjwall spotted that we were being a bit inefficient with our container size by storing the tar before extracting it.

This should be cleaned up and ideally done in a single step by updating the download_bin() method.

For consistency sakes we should also ideally do this on the accumulo-docker repo https://github.com/apache/accumulo-docker/blob/master/Dockerfile