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/bridge/bridge.go

@@ -386,25 +386,30 @@ 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 n.IPMasq {
+	if ipn != nil && n.IPMasq {
 		chain := utils.FormatChainName(n.Name, args.ContainerID)
 		comment := utils.FormatComment(n.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/bridge/bridge_test.go

@@ -273,6 +273,49 @@ var _ = Describe("bridge Operations", func() {
 		})
 	})
 
+	It("deconfigures an unconfigured bridge with DEL", func() {
+		const BRNAME = "cni0"
+		const IFNAME = "eth0"
+
+		_, subnet, err := net.ParseCIDR("10.1.2.1/24")
+		Expect(err).NotTo(HaveOccurred())
+
+		conf := fmt.Sprintf(`{
+    "cniVersion": "0.3.0",
+    "name": "mynet",
+    "type": "bridge",
+    "bridge": "%s",
+    "isDefaultGateway": true,
+    "ipMasq": false,
+    "ipam": {
+        "type": "host-local",
+        "subnet": "%s"
+    }
+}`, BRNAME, subnet.String())
+
+		targetNs, err := ns.NewNS()
+		Expect(err).NotTo(HaveOccurred())
+		defer targetNs.Close()
+
+		args := &skel.CmdArgs{
+			ContainerID: "dummy",
+			Netns:       targetNs.Path(),
+			IfName:      IFNAME,
+			StdinData:   []byte(conf),
+		}
+
+		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())
+	})
+
 	It("configures and deconfigures a bridge and veth with default route with ADD/DEL for 0.1.0 config", func() {
 		const BRNAME = "cni0"
 		const IFNAME = "eth0"