drivers/exec: Account for cgroup-v2 memory stats
drivers/exec: Account for cgroup-v2 memory stats

If the host is running with cgroup-v2, RSS and Max Usage doesn't get
reported anymore.

dvusboy/nomad,burdandrei/nomad,burdandrei/nomad,burdandrei/nomad,burdandrei/nomad,burdandrei/nomad,burdandrei/nomad,burdandrei/nomad,hashicorp/nomad,dvusboy/nomad,hashicorp/nomad,dvusboy/nomad,dvusboy/nomad,dvusboy/nomad,dvusboy/nomad,dvusboy/nomad,hashicorp/nomad,hashicorp/nomad,hashicorp/nomad,hashicorp/nomad