Added additional logging to s3 provider

This is a reasonably trivial commit, but I thought it might help to have a bit of logging output for S3 deploys. We've also had some issues on our (really) long S3 deploys hitting the 10 minute timeout, and though the extra logs might help here?
I wonder if we should extract this to `Provider`. Either as a different method (say, `log_verbose`) or an optional arg to `log` (`def log(message, verbose=false)`).