xfstests: 223 - test file alignment on stripe geometry

xfstests: 223 - test file alignment on stripe geometry

A first-cut test to ensure that files are well-aligned on filesystems
with stripe geometry.

Several sizes of stripe units are mkfs'd, and then files are written
and fallocated in various multiples of those stripe sizes.
Each file is checked to ensure that the first block is
stripe-aligned.

(Ideally, for any fragmented files, we should ensure that each
fragment start is well-aligned, but this does not do that yet)

(slightly unrelated: don't send scratch mkfs output to /dev/null,
we'd like to see mkfs output and direct it to $seq.full - this
more or less matches _scratch_mkfs_xfs behavior and doesn't
break any tests that I can see)

Signed-off-by: Eric Sandeen <sandeen@sandeen.net>
Reviewed-by: Christoph Hellwig <hch@lst.de>