Change in vdsm[master]: storage: Add inplace virt-sparsify support

[Nir Soffer]

Nir Soffer has posted comments on this change.

Change subject: storage: Add inplace virt-sparsify support
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Patch Set 13:

From the discussion with Richard and Kevin, we learned that we can use this only on the top volume in an image. We need to validate that the volume requested by the caller is the leaf volume, and fail the request if not.

We also must prevent usage of this verb on a template image used by any other image. Doing this check safely may be hard since it can be done only on the spm.

Finally we must protect the image during the operation using volume generation and mark the image as illegal, so another host cannot consume this image while we are sparsifying it. See the latest version of copy_data for the details how it is done.