Docker: download binary of patched spark (instead of building with mvn)
Docker: download binary of patched spark (instead of building with mvn)

The prebuild takes up much less space than the assembled project, which will thin the Docker image out
Also, mvn package took so long that our build would occasionally time out on Docker Hub.

TresAmigosSD/SMV,TresAmigosSD/SMV,TresAmigosSD/SMV,TresAmigosSD/SMV