Clean logs from Lambda in CloudWatch

[nateiam]

As a Herd-MDL Administrator I want to view clean, organized logs in the CloudWatch console.

In #17 we introduced lambdas that clean up certain AWS resources when a stack is deleted. Each of these Lambdas writes to its own log groups which looks noisy in the CloudWatch console.

Acceptance Criteria

• Cleanup Lambdas write to their own log stream within the MDL stack parent log group