Remove unnecessary log messages

In spite of it saying 9 commits in my pull request, there's only 2 files or 3-4 lines actually changed. (My git skills aren't strong enough to untangle/simplify the commit messages).

Lowers loglevel for a couple of mysql messages;
- the text format of the innodb output isn't standardised and can change between mysql versions, hence the lowering of missing keys from error to debug;
- don't spam the logfile with connection messages each time