plugins/*: Don't error if the device doesn't exist

I wasn't able to test or update the dhcp plugin but from a code read it
should be fine. All the other plugins are tested and fixed

plugins/main/ptp/ptp.go

@@ -268,25 +268,30 @@ func cmdDel(args *skel.CmdArgs) error {
 		return nil
 	}
 
+	// There is a netns so try to clean up. Delete can be called multiple times
+	// so don't return an error if the device is already removed.
+	// If the device isn't there then don't try to clean up IP masq either.
 	var ipn *net.IPNet
 	err := ns.WithNetNSPath(args.Netns, func(_ ns.NetNS) error {
 		var err error
 		ipn, err = ip.DelLinkByNameAddr(args.IfName, netlink.FAMILY_V4)
+		if err != nil && err == ip.ErrLinkNotFound {
+			return nil
+		}
 		return err
 	})
+
 	if err != nil {
 		return err
 	}
 
-	if conf.IPMasq {
+	if ipn != nil && conf.IPMasq {
 		chain := utils.FormatChainName(conf.Name, args.ContainerID)
 		comment := utils.FormatComment(conf.Name, args.ContainerID)
-		if err = ip.TeardownIPMasq(ipn, chain, comment); err != nil {
-			return err
-		}
+		err = ip.TeardownIPMasq(ipn, chain, comment)
 	}
 
-	return nil
+	return err
 }
 
 func main() {

plugins/main/ptp/ptp_test.go

@@ -111,4 +111,42 @@ var _ = Describe("ptp Operations", func() {
 		})
 		Expect(err).NotTo(HaveOccurred())
 	})
+	It("deconfigures an unconfigured ptp link with DEL", func() {
+		const IFNAME = "ptp0"
+
+		conf := `{
+    "cniVersion": "0.3.0",
+    "name": "mynet",
+    "type": "ptp",
+    "ipMasq": true,
+    "mtu": 5000,
+    "ipam": {
+        "type": "host-local",
+        "subnet": "10.1.2.0/24"
+    }
+}`
+
+		targetNs, err := ns.NewNS()
+		Expect(err).NotTo(HaveOccurred())
+		defer targetNs.Close()
+
+		args := &skel.CmdArgs{
+			ContainerID: "dummy",
+			Netns:       targetNs.Path(),
+			IfName:      IFNAME,
+			StdinData:   []byte(conf),
+		}
+
+		// Call the plugins with the DEL command. It should not error even though the veth doesn't exist.
+		err = originalNS.Do(func(ns.NetNS) error {
+			defer GinkgoRecover()
+
+			err := testutils.CmdDelWithResult(targetNs.Path(), IFNAME, func() error {
+				return cmdDel(args)
+			})
+			Expect(err).NotTo(HaveOccurred())
+			return nil
+		})
+		Expect(err).NotTo(HaveOccurred())
+	})
 })