Adding 'worker' tag to tablet.

When a worker is working on a tablet, add a URL that
points back to the worker.
Comparing row types before the diff now.
Splitting IsServingType.

Into IsInServingGraph for types that are exposed to the serving
graph, and IsRunningQueryService for types that are running
the query service. Easier to individually manipulate them now.
Fixing ListeningURL in servenv. Adding QPS to diff.
Adding a missing close on the listening socket.