Set config.json file changes to Info log level

[vincentmli]

https://github.com/f5devcentral/f5-ctlr-agent/blob/master/f5_ctlr_agent/bigipconfigdriver.py#L584

            if changed:
                log.debug('config file {0} changed - signalling bigip'.format(
                    self._config_file, self._config_stats, sha))
                self._config_stats = sha
                self._on_change()

Please consider use log.info instead of log.debug, config.json files changes is an important information to notify users that something has changed in the cluster or some other reason, since config.json changes would trigger configuration syncing to BIGIP, this is a very important trouble shooting information for customer, the k8s controller debug log is quite chatty, and this log in debug level can be buried and go unnoticed