Print out info on upstream servers for weaveDNS debugging

[bboreham]

When remote troubleshooting it can be useful to know what weave thinks its upstream servers are.

[bboreham]

And it would be useful to log out that there are zero upstream servers, especially if we get asked to resolve an upstream name.

[rade]

it would be useful to log out that there are zero upstream servers, especially if we get asked to resolve an upstream name.

No. Except perhaps at debug log level.

[awh]

weave report all the things

[rade]

I think it's perfectly reasonable to have the upstreams reported in weave status, not just weave report. I am opposed to logging "there are zero upstream servers" every time we attempt to resolve a name upstream.

[darabi]

As a user, I would appreciate a message during startup which clearly states that there are zero upstream servers, making me aware of my mis-configuration. That would have made my life easier and saved @bboreham from my stupid questions on IRC.

In debug mode, I would also appreciate a message like 'cannot resolve name …. in local database and as I don't have upstreams configured, I return a ServFail'.