Export AWS_ACCESS_KEY_ID and AWS_SECRET_ACCESS_KEY

This naming scheme is used by the new official aws-cli client [1], so
hopefully it is becoming somewhat of a standard. It stems from the
underlying boto Python library, so incidentally it automatically serves
other tools like Ansible too.


[1]: https://github.com/aws/aws-cli
Merge pull request #14 from ches/new-auth-vars

Export AWS_ACCESS_KEY_ID and AWS_SECRET_ACCESS_KEY