aws_key_id & aws_sec_key required even when using iam profile

[asbestossupply]

According to the readme (wrt aws_key_id & aws_sec_key)

This parameter is required when your agent is not running on EC2 instance with an IAM Instance Profile.

but in reality it these parameters are always required (see out_kinesis.rb)

for the time being for my own purpose i just removed these two parameters from the validation array but i think this needs a more robust solution.

is there a good way to test if there's a current iam profile in use? thoughts?