webadmin: import vm dialog - fix subtabs refresh

As done in 'ImportVmModel -> initDetailModels',
VmImportDiskListModel/VmImportInterfaceListModel should also override
'setEntity' to get the VM object rather than the wrapping ImportVmData
EntityModel (same applies for TemplateImport models)

Change-Id: Iab5f6f522d007dd88e8d6a14f9ab66f37a1adae4
Bug-Url: https://bugzilla.redhat.com/1141693
Signed-off-by: Daniel Erez <derez@redhat.com>