Add NSID to queries and log results

[pawal]

For anycast deployments, it is very useful to find out which node we we're talking to.

[matsduf]

A specification is to written for this feature.

[sandoche2k]

We have to create a TC first

[matsduf]

This should just be the output of the Engine as a message with DEBUG level, preferably each time a server is queried. It might be that we have to add an interface in Zonemaster-LDNS to see OPT and NSID.