systemd: set systemd KillMode

Change the kill mode to process so that systemd does not kill container
processes when the daemon is shutdown but only the docker daemon

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

contrib/init/systemd/docker.service

@@ -34,5 +34,8 @@ TasksMax=infinity
 # set delegate yes so that systemd does not reset the cgroups of docker containers
 Delegate=yes
 
+# kill only the docker process, not all processes in the cgroup
+KillMode=process
+
 [Install]
 WantedBy=multi-user.target