replace _min_dio_alignment with calls to src/min_dio_alignment

replace _min_dio_alignment with calls to src/min_dio_alignment

Use the min_dio_alignment C tool to check the minimum alignment.
This allows using the values obtained from statx instead of just guessing
based on the sector size and page size.

For tests using the scratch device this sometimes required moving code
around a bit to ensure the scratch device is actually mounted before
querying the alignment.

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