xfstests: fix broken redirects in generic/131

xfstests: fix broken redirects in generic/131

generic/131 attempts to kill processes that may no longer exist when
the test finishes and has a broken redirect for the error messages
and they end up in a file named "1" in the xfstests root instead of
/dev/null.

Not only that, the attempts to redirect stderr to stdout in the
middle of the test use incorrect redirect syntax, so they create an
empty file named "1" in the xfstests root...

IOWs, all the redirects in the test are broken. Fix them and clean
up the failure case to use the exit trap to trigger the cleanup
function....

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Rich Johnston <rjohnston@sgi.com>
Signed-off-by: Rich Johnston <rjohnston@sgi.com>