containerd: add After=dbus.service (#11781)

This is needed for shutdown ordering: while at startup, it's not a
problem that containerd start before dbus (the dbus socket already
exists) it needs to shutdown before dbus to do its cleanup (asking
systemd via dbus to cleanup cgroups).

roles/container-engine/containerd/templates/containerd.service.j2

@@ -15,7 +15,7 @@
 [Unit]
 Description=containerd container runtime
 Documentation=https://containerd.io
-After=network.target local-fs.target
+After=network.target local-fs.target dbus.service
 
 [Service]
 ExecStartPre=-/sbin/modprobe overlay