logging usability tweaks

[beav]

Currently, a warning message is emitted when 'master' is not found on a repo, even though 'main' is tried next. The log level for this is too high and should be at 'info' level, since the user doesn't need to take action or look into anything if 'master' is not found.

Additionally, an info-level message for "trying alternate: main" is displayed, but there is no follow-up message saying if it worked or not. We can guess that it worked since bonfire continues processing but it would be good to be explicit that the branch was found, given the prior log messages.