Allow variations on names for access and secret keys, in keeping with current standards in AWS clients

[robparrott]

The current version of the AWS CLI uses a different naming scheme:

• http://docs.aws.amazon.com/cli/latest/userguide/cli-chap-getting-started.html

In particular the values aws_access_key_id and aws_secret_access_key and region. We should honor those names as well as the older names, since this is quite confusing, with all the clients out there!