Improved UBus supported

- aligned the handling of UBus connections with the DBus code as it
makes it a bit easier to comprehend;
- added logging to the various UBus calls to aid debugging from an
enduser point of view, but be careful to not flood the logs;
- show the (lack of) support for UBus in the configuration string.
diff --git a/src/config.h b/src/config.h
index 203d69e..99b22eb 100644
--- a/src/config.h
+++ b/src/config.h
@@ -362,6 +362,10 @@
 "no-"
 #endif
 "DBus "
+#ifndef HAVE_UBUS
+"no-"
+#endif
+"UBus "
 #ifndef LOCALEDIR
 "no-"
 #endif