275: Fix to test and pass properly
This is a significant rework of 275, which made too many
assumptions about details of space usage and failed on several
filesystems (it passed on xfs, but only by accident).
This new version tries to leave about 256k free, then tries
a single 1M IO, and fails only if 0 bytes are written.
It also sends a lot more to $seq.full for debugging on failure,
doesn't rm -rf $SCRATC_MNT, and fixes a few other stylistic things.
Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>