Spark Docker files usable for testing and development purposes.

These images are intended to be run like so:

docker run -v $SPARK_HOME:/opt/spark spark-test-master
docker run -v $SPARK_HOME:/opt/spark spark-test-worker spark://<master_ip>:7077

Using this configuration, the containers will have their Spark directories mounted to your actual SPARK_HOME, allowing you to modify and recompile your Spark source and have them immediately usable in the docker images (without rebuilding them).