Mem usage (WSS):
The easiest way to get the WSS of a Docker contaier is to ask Docker
using the "docker stats" command.
So I have docker_wrapper do this periodically (10 sec... it's a bit slow).

But how to get this back to the client?
Currently there's no provision for an app to reports its own WSS.
So I added one, by adding an optional field to the app status messages
sent from app to client in shared mem.
If this is present, the client uses it instead of procinfo.

CPU time: "docker stats" reports CPU fraction
(averaged over what period?)
We multiply that by the stats poll.
Not exactly the same as CPU time, but close enough.