Added outputs for generated iam_role resource.

[nielsdraaisma]

This PR exposes the arn/name of the iam_role which is created by this module.

[tfhartmann]

Please accept my apologies for the delay in review on this.
I like the idea of adding the outputs, but this PR looks like it effectively reverts #26 Can I suggest rather then removing the logic for using a custom IAM policy you add a conditional to the output so that it only fires if the module creates the policy? Basically, I'm concerned with potentially loosing a feature of the module. It's also possible that I just misread the diff too...