make 225 use SCRATCH_DEV

make 225 use SCRATCH_DEV

Use the scratch device for test 225 so that both custom mkfs and
mount options impact the test (e.g. filesystem block size). This
exposes test failures when using 512 byte block sizes, which
currently not tested unless the test device is specifically created
with a 512 byte block size.

Also clean up the file names to include the test number, and don't
remove the test files after the test has finished so that it leaves
behind a corpse that can be dissected when the test fails.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Alex Elder <aelder@sgi.com>