Support IAM role based authentication

[guss77]

The simpledb library requires users to provide an AWS keyid and secret, while the underlying aws-lib support creating a client without AWS credentuals - in which case it uses IAM role based authentication for running under EC2.

Simpledb should support logging in without specifying AWS credentials using aws-lib IAM role support.

[darrin]

Hello all - I've implemented a simpleDB key/value store just to test it out. Next step is to look at better storage of json objects as well as the backoff/retry logic - which it looks like you've already implemented. That said - I agree with @guss77 that we should be using IAM roles for auth - security is particularly important for this application. Where are we on this pull request?

[vijayopensource]

any update on this?