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.go

@@ -0,0 +1,13 @@
+// +build linux,cgo
+
+package system
+
+/*
+#include <unistd.h>
+int get_hz(void) { return sysconf(_SC_CLK_TCK); }
+*/
+import "C"
+
+func GetClockTicks() int {
+	return int(C.get_hz())
+}