generic/019: Silence possible kill failure

generic/019: Silence possible kill failure

When the filesystem is force-killed in generic/019 and fsstress is
compiled with DEBUG then it's possible for check_cwd() to fail. In
this case fsstress would just die and invoking kill on its pid would
produce an error to the output file:

	+./tests/generic/019: line 157: kill: (32750) - No such process

Fix this possibility by ignoring the result of the output command,
this won't affect the test coverage.

Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: Eryu Guan <eguan@redhat.com>
Signed-off-by: Eryu Guan <eguan@redhat.com>