WiP: feat(xo-server/delta backup): handle VDI migration

[julien-f]

Fixes #2896

Store its UUID in metadata to avoid a delta afteter a migration.

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[julien-f]

It does not work, it appears XAPI empty other_config when migrating the VDI…

Requires more testing.

[julien-f]

@olivierlambert Do you want to do something about this in XCP-ng?

[olivierlambert]

Not sure to understand. I'm currently in a meeting. Ask @stormi

[stormi]

Do you mean modifying the XAPI?

[julien-f]

@stormi yes.

We are trying to save the original UUID of a VDI in it's other_config property to avoid having to fall back to a full copy when it changed (in case of SR migration for instance).

Unfortunately, it appears (more tests required) that other_config is emptied when the VDI is migrating, defeating the purpose.

[olivierlambert]

So we should test if there's a field that's preserved after a VDI migration.