common/populate: use metadump v2 format by default for fs metadata snapshots

common/populate: use metadump v2 format by default for fs metadata snapshots

When we're snapshotting filesystem metadata after creating a populated
filesystem, force the creation of metadump v2 files by default to
exercise the new format, since xfs_metadump continues to use the v1
format unless told otherwise.

Signed-off-by: "Darrick J. Wong" <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Zorro Lang <zlang@kernel.org>