Improve debugging for resolver
Improve debugging for resolver

This patch improves debugging for the resolver;

- prefix debug messages with `[resolver]` for easier finding in the daemon logs
- use `A` / `AAAA` for query-types in the logs instead of their numeric code
- add debug messages if the external DNS did not return a result
- print sucessful results (t.b.d.)

Signed-off-by: Sebastiaan van Stijn <64b2b6d12bfe4baae7dad3d018f8cbf6b0e7a044@gone.nl>

mahak/libnetwork,vdemeester/libnetwork,mahak/libnetwork,vdemeester/libnetwork,fcrisciani/libnetwork,medallia/libnetwork,medallia/libnetwork,vdemeester/libnetwork,mahak/libnetwork,medallia/libnetwork,abhi/libnetwork,allencloud/libnetwork,docker/libnetwork,abhi/libnetwork,kolyshkin/libnetwork,kolyshkin/libnetwork,docker/libnetwork,fcrisciani/libnetwork,abhi/libnetwork,kolyshkin/libnetwork,docker/libnetwork,ityangchen/libnetwork,allencloud/libnetwork,ityangchen/libnetwork