Improve the clarity and conciseness of our logging

[alaric-dotmesh]

User requirement

As the manager of a dotmesh installation, I want clearer logs so that I can more easily tell what's going on.

Key acceptance criteria

• [ ] It should be easy to see what's overally happening with a quick skim through the logs.
• [ ] It should be easy to find specific things (eg, errors, "the bit where it did operation X", etc)

Previous work with putting out useful headings in the logs output by the acceptance test suite helped with those; apply the same logic to the dotmesh server logs, removing superfluous things, giving bigger events more prominence, making similar types of events similar log lines so they can be seen as peers, that sorta thing.

[alaric-dotmesh]

This is a principle rather than a task, and we're doing it, so I'm going to close this.