test: Rename TestStorageVDO to TestStorageLegacyVDO
test: Rename TestStorageVDO to TestStorageLegacyVDO

The `vdo cli` API and standalone "vdo" block device type has been
deprecated a while ago, in favor of the LVM/udisks-lvm2 API. The latter
is the officially documented one [1].

Rename the corresponding test class, so that we can rebuild the coverage
with the new API.

[1] https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/8/html/deduplicating_and_compressing_logical_volumes_on_rhel/creating-a-deduplicated-and-compressed-logical-volume_deduplicating-and-compressing-logical-volumes

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