Use instance role instead of added AWS_ACCESS_KEY_ID properties

[jankronquist]

Adding AWS_ACCESS_KEY_ID and AWS_SECRET_KEY reveals my personal access keys to everyone else in the organisation that have access to beanstalk.

Instead the instance should the access key and secret provided by the role that is assigned to the instance:

http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/iam-roles-for-amazon-ec2.html

This is automatically used by the Java libraries and therefore also by for instance amazonica.