#9356 Add cite to IAM for EC2 credential sharing.

1.Per research on #9356, I found a blog so added reference to it to the tutorial.
2.The master already had removed the specific reference to insecure method; "If you are spooling up minions on EC2, you could pass them in using user_data or a cloud-init script. If you are handing them off to a team of developers for provisioning dev machines, you will need a secure file transfer.".