In preparation for
RFC-782, clean up some log usage to make it conform better with python logging. All changes will be compatibility with lsst.log.
- Changing log.warn to log.warning (the former is deprecated in python and lsst.log supports both)
- Fixing cases where string interpolation is happening before the logger decides whether to deliver the message.
- Switch away from the infof/warnf approach that Python never accepted (in python % vs f formatting is set per-logger).