Added cns utils.go (#102)

Author: tamilmani1989

cns/common/utils.go

@@ -0,0 +1,29 @@
+package common
+
+import (
+	"fmt"
+	"os/exec"
+
+	"github.com/Azure/azure-container-networking/log"
+)
+
+func ExecuteShellCommand(command string) error {
+	log.Printf("[Azure-CNS] %s", command)
+	cmd := exec.Command("sh", "-c", command)
+	err := cmd.Start()
+	if err != nil {
+		return err
+	}
+	return cmd.Wait()
+}
+
+func SetOutboundSNAT(subnet string) error {
+	cmd := fmt.Sprintf("iptables -t nat -A POSTROUTING -m iprange ! --dst-range 168.63.129.16 -m addrtype ! --dst-type local ! -d %v -j MASQUERADE",
+		subnet)
+	err := ExecuteShellCommand(cmd)
+	if err != nil {
+		log.Printf("SNAT Iptable rule was not set")
+		return err
+	}
+	return nil
+}