Bug#939551: systemd MountFlags broken

[Harald Dunkel]

Package: systemd
Version: 241-5

systemd in Buster and older fails to handle MountFlags correctly,
see

https://github.com/systemd/systemd/commit/37ed15d7edaf59a1fc7c9e3552cd93a83f3814ef

This seriously affects the "containerd" versions of Docker >= 18.09.
On installing Rancher (just as an example) I got an error message saying


	Failed to bring up Worker Plane: [Failed to start [kubelet]
	container on host [r01]: Error response from daemon: path
	/var/lib/kubelet is mounted on / but it is not a shared mount]


Host r01 is running Buster (systemd 241-5, docker 18.09).

Would it be possible to cherrypick this fix for Buster and
Stretch?

Thanx in advance
Harri