utils: Retrieval of managed objects of DBUS

This commit implements functionality to retrieve the managed object of a
specific DBUS service on a particular path.  Additionally implements a
function template for inventory objects which efficiently enables
retrieval of managed object for Inventory Manager.

Tested: Added unit test cases for checking the return value.

Change-Id: Ide652f843db1623bdacebf3e269e03895bbb7f1a
Signed-off-by: Riya Dixit <riyadixitagra@gmail.com>