[Migrated] Migrate bash script to tox

[jneves]

Originally from: Miserlou/Zappa#1230 by bxm156

Description

1. Migrated ./test.sh to tox
2. Fixed a flaky test
3. Updated Readme
4. Switched to the newer/preferred coverage invocation.

GitHub Issues

Relates/Fixes #813

[github-actions]

Hi there! Unfortunately, this Issue has not seen any activity for at least 90 days. If the Issue is still relevant to the latest version of Zappa, please comment within the next 10 days if you wish to keep it open. Otherwise, it will be automatically closed.

[github-actions]

Hi there! Unfortunately, this Issue was automatically closed as it had not seen any activity in at least 100 days. If the Issue is still relevant to the latest version of Zappa, please open a new Issue.