systemctl: downgrade log level of ECONNREFUSED from system dbus.service

To suppress log message when 'systemctl poweroff' or friends invoked in
rescue shell, which does not have dbus.service.

src/systemctl/systemctl-util.c

@@ -32,7 +32,7 @@
 
 static sd_bus *buses[_BUS_FOCUS_MAX] = {};
 
-int acquire_bus(BusFocus focus, sd_bus **ret) {
+int acquire_bus_full(BusFocus focus, bool graceful, sd_bus **ret) {
         int r;
 
         assert(focus < _BUS_FOCUS_MAX);
@@ -54,7 +54,8 @@ int acquire_bus(BusFocus focus, sd_bus **ret) {
                 else
                         r = bus_connect_transport(arg_transport, arg_host, arg_runtime_scope, &buses[focus]);
                 if (r < 0)
-                        return bus_log_connect_error(r, arg_transport, arg_runtime_scope);
+                        return bus_log_connect_full(graceful && focus == BUS_FULL && r == -ECONNREFUSED ? LOG_DEBUG : LOG_ERR,
+                                                    r, arg_transport, arg_runtime_scope);
 
                 (void) sd_bus_set_allow_interactive_authorization(buses[focus], arg_ask_password);
         }