Add tests and automated CI

[busunkim96]

Samples in this repository are used in several published Google Cloud tutorials.

Some directories have no tests and others have test coverage that may be too low to properly meet the user journey testing requirement, leading to issues like #382.

Tasks:

• Add tests to all subdirectories.
• Check tests to make sure they sufficiently test the user journey.
• Check test infrastructure - it should ideally closely match what is in https://github.com/googlecloudplatform/python-docs-samples for easier maintainability
  • Periodic job should run nightly with flakybot enabled so we know when something breaks

CC @danoscarmike @parthea

[danoscarmike]

@busunkim96 @parthea please prioritize this one between you 🙏🏻

[busunkim96]

@parthea 👋 Why did you change this to cleanup? IIRC I set this as bug after discussing with Dan, since the likelihood of forgetting about cleanup issues is higher.