Refactor getManagedObjects method

Since the getManagedObjects method has been implemented in
dbus_utility and this commit is to integrate all the places where the
GetManagedObjects method is obtained, and use the method in
dbus_utility uniformly.

Signed-off-by: George Liu <liuxiwei@inspur.com>
Change-Id: Ic13f2bef7b30f805cd3444a75d7df17b031f2eb0
diff --git a/include/nbd_proxy.hpp b/include/nbd_proxy.hpp
index e4d709b..62bd324 100644
--- a/include/nbd_proxy.hpp
+++ b/include/nbd_proxy.hpp
@@ -327,15 +327,13 @@
 {
     BMCWEB_LOG_DEBUG << "nbd-proxy.onopen(" << &conn << ")";
 
-    auto openHandler =
+    sdbusplus::message::object_path path("/xyz/openbmc_project/VirtualMedia");
+    dbus::utility::getManagedObjects(
+        "xyz.openbmc_project.VirtualMedia", path,
         [&conn](const boost::system::error_code& ec,
                 const dbus::utility::ManagedObjectType& objects) {
         afterGetManagedObjects(conn, ec, objects);
-    };
-    crow::connections::systemBus->async_method_call(
-        std::move(openHandler), "xyz.openbmc_project.VirtualMedia",
-        "/xyz/openbmc_project/VirtualMedia",
-        "org.freedesktop.DBus.ObjectManager", "GetManagedObjects");
+        });
 
     // We need to wait for dbus and the websockets to hook up before data is
     // sent/received.  Tell the core to hold off messages until the sockets are