special treatment to stop underlying docker container if running via shim?

[yarikoptic]

follow up to datalad/datalad-container#144
where I tried just to kill our shim but docker container seems remain running:

(git-annex)lena:~/.tmp/repro-6XkWWkE/ds000003-qc[master]git-annex
$> containers/scripts/singularity_cmd: line 1: warning: wait_for: recursively setting old_sigint_handler to wait_sigint_handler: running_trap = 1

$> kill 3217993
kill: kill 3217993 failed: no such process

$> docker ps
CONTAINER ID        IMAGE                             COMMAND                  CREATED             STATUS              PORTS               NAMES
39e56a15687a        repronim-containers-sing:latest   "/entrypoint.sh run …"   5 minutes ago       Up 5 minutes                            practical_gagarin