Fewer layers in docker images

[ash211]

#320 (comment)

Basically, don't repeatedly use RUN

[johscheuer]

Hi, I stumbled over this issue (I want to learn more about Spark on Kubernetes) and wanted to fix this issue. After I looked into the Dockerfiles I found out that there are many repetitions in the Docker images maybe it would be a good move to create a base-image ?

[mccheah]

Using a base image would be helpful - can you push something for review? SparkDockerImageBuilder would need changes as well.

[ash211]

@johscheuer thanks for taking an interest in this project!

We can do this by merging the RUN commands in each separate Dockerfile, and then later creating a base-image, or jumping straight to creating the base image.

If you're interested in contributing to this project with a PR I'd be happy to help code review!