vdi: Fix .bdrv_has_zero_init()

vdi: Fix .bdrv_has_zero_init()

Static VDI images cannot guarantee to be zero-initialized.  If the image
has been statically allocated, forward the call to the underlying
storage node.

Reported-by: Stefano Garzarella <[email protected]>
Signed-off-by: Max Reitz <[email protected]>
Reviewed-by: Stefan Weil <[email protected]>
Acked-by: Stefano Garzarella <[email protected]>
Tested-by: Stefano Garzarella <[email protected]>
Message-id: 20190724171239[email protected]
Reviewed-by: Maxim Levitsky <[email protected]>
Signed-off-by: Max Reitz <[email protected]>