Use cgo to get systems clock ticks for metrics

Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@crosbymichael.com> (github: crosbymichael)

system/sysconfig_nocgo.go

@@ -0,0 +1,9 @@
+// +build linux,!cgo
+
+package system
+
+func GetClockTicks() int {
+	// when we cannot call out to C to get the sysconf it is fairly safe to
+	// just return 100
+	return 100
+}