use mocks in tests for external github API calls

[kcranston]

There are several places in the code where we call github via the API. This code has no test coverage right now (to avoid calling the API each time we run the test suite and running into API rate limits). Ideally, we would mock the github response and / or local changes in tests that include a github call. This includes any code that calls the following methods in github.py:

• remote_repo_exists
• clone_repo
• create_repo
• push_to_github
• pull_from_github

[lwasser]

🐒