nginx-aws-signature: test framework implementation

[shawnhankim]

As an API/App Developer,

I want to make sure any change does not block the existing features of nginx-aws-signature library based on test framework. In the meantime, I want to ensure that it is always interoperable with other module such as nginx-s3-gateway and nginx-lambda-gateway.

AC:

• Implement unit test framework by refactoring nginx-s3-gateway/test/unit.
• Implement integration test framework by refactoring nginx-s3-gateway/test/integration.
• Local test framework based on Docker containers by refactoring nginx-s3-gateway/docker-compose