Improve logging coverage and flexibility

[tgross]

In #28, debugging the problem could have been improved by having better logging in the preStart handler. Also, in #28 (comment) @tgross wrote:

It looks like there's a couple spots we could hook in more logging too. The balance of debug vs info has been hard to get right; I'm wondering if we should keep the last N messages of a DEBUG level in a ring log with some mechanism to dump them to stdout even if the instances are logging at INFO.

Because we don't have a persistent daemon for the manage.py this might be easier said than done. We could always just have a file that we truncate if it gets above size N. Or perhaps just move all the logging around replication setup to INFO, although I'm not wild about that solution either.

[tgross]

Released in https://github.com/autopilotpattern/mysql/releases/tag/5.6r2.3.0