Outdated HAProxy processes can affect request routing

[cdonati]

We currently rely on HAProxy's -sf flag along with the accuracy of the pidfile to ensure that older processes are stopped gracefully. This is not always entirely effective, and if appservers start on the old referenced locations, requests can get routed to the wrong version.

The RoutingManager should keep track of HAProxy processes in a cgroup so that it can ensure older processes do not stick around.