webadmin: VmSnapshotList - filter LunDisks on getVmDiskList

VmSnapshotList -> updatePreviewedDiskSnapshots:
filer LunDisks from 'getVmDiskList' result.

Change-Id: Iaf983d1a8095b8739cd0e4ff4a872100f3e2c921
Bug-Url: https://bugzilla.redhat.com/1148424
Signed-off-by: Daniel Erez <derez@redhat.com>