core: soundcard not persisted on new instance type

The problem was that the sondcard was persisted only when there was a cluster.
This is not the case for the instance type. Solved the same way as for the new
instance type (sending null cluster version).

Change-Id: I81d0adf9f8873e2e0b9c1a28c068c2de4ad59751
Bug-Url: https://bugzilla.redhat.com/1124270
Signed-off-by: Tomas Jelinek <tjelinek@redhat.com>