To facilitate porting over to glib, this rewrites the auto cleanup
macros to use glib's equivalent.

As a result it is now possible to use g_autoptr/VIR_AUTOPTR, and
g_auto/VIR_AUTOCLEAN, g_autofree/VIR_AUTOFREE interchangably, regardless
of which macros were used to declare the cleanup types.

Within the scope of any single method, code must remain consistent
using either GLib or Libvirt macros, never mixing both. New code
must preferentially use the GLib macros, and old code will be
converted incrementally.
Reviewed-by: NJán Tomko <jtomko@redhat.com>
Signed-off-by: NDaniel P. Berrangé <berrange@redhat.com>