ItemUpdater: Only create the dbus objects for Host and System images

Get the version purpose property from the signal and
only process the version objects that have a purpose of Host or
System (combined image).

Change-Id: If0180f7fcbd2ecde6b885d6e5dc67379dc223e18
Signed-off-by: Adriana Kobylak <anoo@us.ibm.com>
diff --git a/item_updater.hpp b/item_updater.hpp
index 216b1d7..97f5005 100755
--- a/item_updater.hpp
+++ b/item_updater.hpp
@@ -28,7 +28,7 @@
          */
         ItemUpdater(sdbusplus::bus::bus& bus, const std::string& path) :
                     ItemUpdaterInherit(bus, path.c_str()),
-                    busItem(bus),
+                    bus(bus),
                     versionMatch(
                             bus,
                             MatchRules::interfacesAdded() +
@@ -67,7 +67,7 @@
         static int validateSquashFSImage(const std::string& versionId);
 
         /** @brief Persistent sdbusplus DBus bus connection. */
-        sdbusplus::bus::bus& busItem;
+        sdbusplus::bus::bus& bus;
 
         /** @brief Persistent map of Activation dbus objects and their
           * version id */