Add a flag to enable systemd cgroups support in runc

Signed-off-by: Mrunal Patel <mrunalp@gmail.com>

main.go

@@ -79,6 +79,10 @@ func main() {
 			Value: "criu",
 			Usage: "path to the criu binary used for checkpoint and restore",
 		},
+		cli.BoolFlag{
+			Name:  "systemd-cgroup",
+			Usage: "enable systemd cgroup support, expects cgroupsPath to be of form \"slice:prefix:name\" for e.g. \"system.slice:runc:434234\"",
+		},
 	}
 	app.Commands = []cli.Command{
 		checkpointCommand,