The CreatedAt date was determined from the volume's `_data`
directory (`/var/lib/docker/volumes/<volumename>/_data`).
However, when initializing a volume, this directory is updated,
causing the date to change.
Instead of using the `_data` directory, use its parent directory,
which is not updated afterwards, and should reflect the time that
the volume was created.
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
Signed-off-by: Paweł Gronowski <pawel.gronowski@docker.com>
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