MXS-2546 Add DNS-resolving to topology detection

When matching hostnames between MaxScale server configuration and the
SHOW SLAVE STATUS-output, use DNS-resolution if a simple string comparison
doesn't find an answer. Results of the resolution are saved to avoid
repeating the operation for the same address.

server/core/session.cc

@@ -766,7 +766,7 @@ json_t* session_json_data(const Session* session, const char* host, bool rdns)
         auto remote = session->client_dcb->remote;
         if (rdns)
         {
-            maxbase::reverse_dns(remote, &result_address);
+            maxbase::reverse_name_lookup(remote, &result_address);
         }
         else
         {