spark-2.0-preview image is built from https://github.com/depend/spark-jobserver/tree/spark-2.0-preview which tracks upstream.
This image is almost identical to the awesome https://hub.docker.com/r/velvia/spark-jobserver/, but with different OS and JRE.
Other versions are self explanatory from the tag naming.
There is no Dockerfile for now because spark-jobserver uses sbtdocker to create Docker images during build process. However I do plan to add some build task to extract Dockerfile soon.