Fix query average measurment and average text output.

The query_ended() call was not in the right spot. Tests did not
detect it. Changed textual output to reflect the fact that they
are for RWSplit reads.

server/modules/routing/readwritesplit/rwsplit_select_backends.cc

@@ -302,7 +302,7 @@ static void log_server_connections(select_criteria_t criteria, const SRWBackendL
                 maxbase::Duration response_ave(server_response_time_average(b->server));
                 std::ostringstream os;
                 os << response_ave;
-                MXS_INFO("Average response time : %s from \t[%s]:%d %s",
+                MXS_INFO("adaptive avg. select time: %s from \t[%s]:%d %s",
                          os.str().c_str(),
                          b->server->address,
                          b->server->port,