Support CodeBuild projects that only write logs to S3

[jlhood]

CodeBuild now supports writing logs to S3 in addition to or instead of CloudWatch logs. This app should be updated to work in the case that the CodeBuild project is configured to only write to S3 with CloudWatch logs disabled.

CodeBuild writes the logs to a gzipped S3 file. This app should be able to copy an unzipped version of the file to the app's S3 bucket for PR contributors to view.

[jlhood]

Unfortunately, BatchGetBuilds output doesn't return bucket and object key of the log file directly in the output. They have a s3DeepLink output parameter that contains an http link to the object. Current workaround is to parse the deep link to find the bucket and key. The app will also have to take the bucket as a parameter so it can setup IAM permissions to allow the Lambda function to read from that bucket.