Config / testing TODOs

[jhamman]

In #75, @norlandrhagen and I have been adding support for Donfig and developing a clearer api for the Runtimes in this project. The following lists some outstanding todos that we should follow up on:

config

• use donfig's expand_environment_variables method to connect to azure's connection string environment variable

testing

• move fixtures.py to conftest.py
• figure out how to set config in a test fixture
• figure out a way to test the CloudRuntime, perhaps use pytest-mock?