S3: Using environment variables for authentication

[nmaguiar]

Describe the bug
When deploying the oPack S3 on an AWS environment where the credentials are environment variables based it will end in error trying to access IAM-role credentials.

To Reproduce
Steps to reproduce the behavior:

1. Create a AWS Lambda function with the AWSLambdaLayers oPack
2. Associate the necessary permissions to access a S3 bucket
3. Write a script or oJob that performs a simple var s3 = new S3(); s3.listObjects("my-bucket")
4. Running se.listObjects will produce the error

Expected behavior
Should try first to use io.minio.credentials.AwsEnvironmentProvider before io.minio.credentials.IamAwsProvider since MinIO client seems not to do it.

[nmaguiar]

Should use a ChainedProvider as per example https://github.com/minio/minio-java/blob/master/examples/MinioClientWithChainedProvider.java