fuzzy: don't use killall

fuzzy: don't use killall

Having test cleanup call 'killall xfs_io fsx xfs_scrub' results in a
system wide process kill, rather than just the processes the test is
running directly.

Make sure we only kill processes the fuzz test directly owns. We can
do this with 'pkill --parent $$ <process names>' to limit the search
for processes to kill to just the children of the current process.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Zorro lang <zlang@redhat.com>
Signed-off-by: Zorro Lang <zlang@kernel.org>