nm-object: delay object property completion until the objects are initialized

nm-object: delay object property completion until the objects are initialized

We don't want to update the properties until the objects referred are complete.
Otherwise the clients get confused. Very confused:

https://bugzilla.redhat.com/show_bug.cgi?id=1313866

We already delay the notification signals. Let's replace that with delaying the
actual ObjectCreatedData processing instead.