generic/038: kill background threads on interrupt

generic/038: kill background threads on interrupt

When I ctrl-c g/038, it either does nothing or it leaves processes
running in the background. It is not cleaning up it's background
processes correctly, so add kill vectors into the cleanup. Make sure
we only kill in the cleanup trap if the background processes are
running.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Zorro Lang <zlang@kernel.org>