Adding /proc/timer_list to the masked paths list

/proc/timer_list seems to leak information about the host. Here is
an example from a busybox container running on docker+kubernetes.

 # cat /proc/timer_list | grep -i -e kube
 <ffff8800b8cc3db0>, hrtimer_wakeup, S:01, futex_wait_queue_me, kubelet/2497
 <ffff880129ac3db0>, hrtimer_wakeup, S:01, futex_wait_queue_me, kube-proxy/3478
 <ffff8800b1b77db0>, hrtimer_wakeup, S:01, futex_wait_queue_me, kube-proxy/3470
 <ffff8800bb6abdb0>, hrtimer_wakeup, S:01, futex_wait_queue_me, kubelet/2499

Signed-Off-By: Davanum Srinivas <davanum@gmail.com>
Signed-off-by: Davanum Srinivas <davanum@gmail.com>

oci/defaults_linux.go

@@ -81,6 +81,7 @@ func DefaultSpec() specs.Spec {
 		MaskedPaths: []string{
 			"/proc/kcore",
 			"/proc/latency_stats",
+			"/proc/timer_list",
 			"/proc/timer_stats",
 			"/proc/sched_debug",
 		},