xfs: test reproducible builds

With the addition of the `-p` populate option, SOURCE_DATE_EPOCH and
DETERMINISTIC_SEED support, it is possible to create fully reproducible
pre-populated filesystems. We should test them here.

[zlang: use _run_fsstress]

Signed-off-by: Luca Di Maio <luca.dimaio1@gmail.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Zorro Lang <zlang@redhat.com>
Signed-off-by: Zorro Lang <zlang@kernel.org>