Port networking to CNI

Replaced netns utility with CNI plugins to create a bridge network
and allow communication between containers with firewall plugin.

Overwrite the CNI config in case it exists. Allow updating the config
on new versions.

Signed-off-by: Carlos de Paula <me@carlosedp.com>

vendor/github.com/containerd/go-cni/README.md

@@ -0,0 +1,60 @@
+[![Build Status](https://travis-ci.org/containerd/go-cni.svg?branch=master)](https://travis-ci.org/containerd/go-cni) [![GoDoc](https://godoc.org/github.com/containerd/go-cni?status.svg)](https://godoc.org/github.com/containerd/go-cni)
+
+# go-cni
+
+A generic CNI library to provide APIs for CNI plugin interactions. The library provides APIs to:
+
+- Load CNI network config from different sources  
+- Setup networks for container namespace
+- Remove networks from container namespace
+- Query status of CNI network plugin initialization
+
+go-cni aims to support plugins that implement [Container Network Interface](https://github.com/containernetworking/cni)
+
+## Usage
+```go
+func main() {
+	id := "123456"
+	netns := "/proc/9999/ns/net"
+	defaultIfName := "eth0"
+	// Initialize library
+	l = gocni.New(gocni.WithMinNetworkCount(2),
+		gocni.WithPluginConfDir("/etc/mycni/net.d"),
+		gocni.WithPluginDir([]string{"/opt/mycni/bin", "/opt/cni/bin"}),
+		gocni.WithDefaultIfName(defaultIfName))
+	
+	// Load the cni configuration
+	err:= l.Load(gocni.WithLoNetwork, gocni.WithDefaultConf)
+        if err != nil{
+		log.Errorf("failed to load cni configuration: %v", err)
+		return 
+	}
+	
+	// Setup network for namespace.
+	labels := map[string]string{
+		"K8S_POD_NAMESPACE":          "namespace1",
+		"K8S_POD_NAME":               "pod1",
+		"K8S_POD_INFRA_CONTAINER_ID": id,
+	}
+	result, err := l.Setup(id, netns, gocni.WithLabels(labels))
+	if err != nil {
+		log.Errorf("failed to setup network for namespace %q: %v",id, err)
+		return 
+	}
+	
+	// Get IP of the default interface
+	IP := result.Interfaces[defaultIfName].IPConfigs[0].IP.String()
+	fmt.Printf("IP of the default interface %s:%s", defaultIfName, IP)
+}
+```
+
+## Project details
+
+The go-cni is a containerd sub-project, licensed under the [Apache 2.0 license](./LICENSE).
+As a containerd sub-project, you will find the:
+
+ * [Project governance](https://github.com/containerd/project/blob/master/GOVERNANCE.md),
+ * [Maintainers](https://github.com/containerd/project/blob/master/MAINTAINERS),
+ * and [Contributing guidelines](https://github.com/containerd/project/blob/master/CONTRIBUTING.md)
+
+information in our [`containerd/project`](https://github.com/containerd/project) repository.