bus: Add missing sd_bus_open() equivalent

Change-Id: I8181dc8932353e8f37da9fab168f34f214d222c0
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/sdbusplus/bus.hpp.in b/sdbusplus/bus.hpp.in
index 587d10b..d3a2605 100644
--- a/sdbusplus/bus.hpp.in
+++ b/sdbusplus/bus.hpp.in
@@ -543,6 +543,13 @@
 }
 
 /* WARNING: THESE ARE NOT THE FUNCTIONS YOU ARE LOOKING FOR! */
+inline bus new_bus()
+{
+    sd_bus* b = nullptr;
+    sd_bus_open(&b);
+    return bus(b, std::false_type());
+}
+
 inline bus new_user()
 {
     sd_bus* b = nullptr;