snapshots and pvcs: test and support arbitrary deletion order

[pohly]

From #297 (comment):

We discussed this a bit further on Monday. @msau42 pointed out that it is valid when a CSI driver refuses to delete PVCs that have snapshots. It is also valid to refuse deleting snapshots when there is still a PVC. In other words, a CSI driver only needs to support one order of deletions, but not both.

This means that picking LIFO order will work for some drivers, but not all.

The right approach is to retry deletion after it failed once, i.e. try to delete snapshot, delete pvc, then if snapshot deletion failed, try again. I think this can be added relatively easily by iterating twice over all resources instead of just once.

We also discussed writing tests that explicitly cover both deletion orders. One test can do "delete snapshot, delete pvc, delete snapshot again (if necessary)", the other "delete pvc, delete snapshot, delete pvc again (if necessary)". This then works with all drivers and ensures that both is tested. But this should be added in a separate PR.

[pohly]

/assign @timoreimann

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[timoreimann]

/assign

[timoreimann]

I'll try to work on this one soon.

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[pohly]

/remove-lifecycle stale

@timoreimann ping...

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[pohly]

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