HintRouter: cleanup + statistics for diagnosis entrypoint

General code cleanup. Routing error detection now more robust.
Remove some unused code. Debug messages now use "unique_name" when
referring to servers.

server/modules/routing/hintrouter/hintrouterdefs.hh

@@ -17,8 +17,12 @@
 #include <maxscale/dcb.h>
 #include <maxscale/log_manager.h>
 
+#if defined(SS_DEBUG)
 #define DEBUG_HINTROUTER
 //#undef DEBUG_HINTROUTER
+#else
+#undef DEBUG_HINTROUTER
+#endif
 
 #ifdef DEBUG_HINTROUTER
 #define HR_DEBUG(msg, ...) MXS_NOTICE(msg, ##__VA_ARGS__)