core: Fix for VmBase

Fix for patch: I9ccb4fc0b807c77bc17cfe02903341cdf4e51d54
Removed 'final' from disk list to allow RPC Serialization.

Change-Id: Id3aa95b2c93fb9cd3cc737f88b8a9ac970d42ba3
Signed-off-by: Ofri Masad <omasad@redhat.com>