sg: Add a verbose flag (-v) to print more debug information

Created by: mrnugget

@courier-new reported a problem with hot-reloading of enterprise-frontend: sometimes it wouldn't start back up again. No "running..." message printed. I suspect that this is because the old process doesn't want to exit. The question is just: why?

So, this starts something that I think we should do anyway: the ability to print debug output.

With sg -v start batches this now prints when sg waits for the previous command to exit.

Later we can add more verbose/debug information, of course. But I'd love to get this in so that @courier-new can start to use this.