Package tests in a docker container

[acmiyaguchi]

The current testing environment requires setting up SPARK_HOME and PYTHONPATH, then installing the proper dependencies before being able to run tests. python_moztelemetry uses docker to encapsulate the testing environment, and is easy to set up.

https://github.com/mozilla/python_moztelemetry/blob/master/Dockerfile
https://github.com/mozilla/python_moztelemetry/blob/master/runtests.sh

This project might benefit from setting up the environment in a similar fashion.