Improve testing of the code that interacts with GitHub

[mockitoguy]

Let's improve testing of the code that interacts with GitHub so that we have decent coverage for this critical functionality.

• Currently we have 2 integration tests that hit GitHub API. Both tests are ignored (search in codebase for @Ignore flag). We should make those tests use example repo instead of real mockito repo and enable the tests. Mockito repo is big and hence the tests are slow. Also, Mockito repo is a real project with real issues reported, it would be better to use mockito-release-tools-example project as target for remote requests to GitHub API.
• We can also create a test that mocks GitHub API, check-in stub JSON result and have neat unit tests for the code.