Use "-t 0" with "docker stop"

The standard Ubuntu 22.04 docker image does not terminate when
SIGTERM is sent to its init process.  (Older Ubuntu docker images did do
that.)  So don't wait 10 seconds before sending the SIGKILL; just do it
right away.

docker/stop-docker

@@ -1,6 +1,6 @@
 #!/bin/bash
 
-docker stop prac_p0 &
-docker stop prac_p1 &
-docker stop prac_p2 &
+docker stop -t 0 prac_p0 &
+docker stop -t 0 prac_p1 &
+docker stop -t 0 prac_p2 &
 wait