Clear log files when re-building locally

[fschutt]

If I am rebuilding my application via spin build --up to rebuild locally, the logs don't get cleared when the server restarts, which is annoying. By default they should be cleared, because I want to simulate how the server reacts on a new deployment.

Maybe there can be a config flag for users who really want this behavior, but by default I'd expect the logs to clear when rebuilding and re-starting the sever.