xfstests: update test 250 and its golden output

xfstests: update test 250 and its golden output

Test 250 actually runs now that it has golden output defined.  The
output the test produces doesn't match the golden output, however.

The main reason seems to be a oversight in the test--the stderr
output of mkfs wasn't being ignored as it should be (likely for
debugging).  Remove the comment character so the stderr does get
ignored.

Doing this still leaves some other output, but since it's filtered
there's no reason to leave it out of the golden output.  So add
the expected result of filtering into the golden output file.

Finally, this test--unlike almost all of the others--specifies the
value of its "tmp" variable as a relative rather than absolute
path.  I'm sure that works in some places, but it produces errors
for me.  Follow the "tmp=/tmp/$$" convention used elsewhere.

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