Get status code from AWS Chalice response

[tianchu]

What does this PR do?

Fix AttributeError: 'Response' object has no attribute 'get' when used in an AWS Chalice project by making the code more robust. AWS Chalice function returns a Response object instead of a dict.

Motivation

Make datadog-lambda work for AWS Chalice projects.

Testing Guidelines

Additional Notes

Types of Changes

• Bug fix
• New feature
• Breaking change
• Misc (docs, refactoring, dependency upgrade, etc.)

Check all that apply

• This PR's description is comprehensive
• This PR contains breaking changes that are documented in the description
• This PR introduces new APIs or parameters that are documented and unlikely to change in the foreseeable future
• This PR impacts documentation, and it has been updated (or a ticket has been logged)
• This PR's changes are covered by the automated tests
• This PR collects user input/sensitive content into Datadog
• This PR passes the integration tests (ask a Datadog member to run the tests)

[DylanLovesCoffee]

LGTM 👍