Downgrading no file warning to an info message

This is a normal condition in event generation, and the metadata peeker is called by the AMI tag helper, which is called in event generation in order to write an AMI tag for the first time (which is reasonable to me). The alternatives would be to detect somehow that evgen is running and conditionally disable the warning, or to pass the information along the tool chain, both of which I think are a bit more invasive and unattractive, but if folks disagree we can give it a try!