Adds support for Multus (multiple interfaces) CNI plugin (#3166)

* Adds support for Multus (multiple interfaces) CNI plugin

Multus is a latin word for "Multi". As the name suggests, it acts as a
Multi plugin in Kubernetes and provides multiple network interface
support in a pod. Multus uses the concept of invoking delegates by
grouping multiple plugins into delegates and invoking them in the
sequential order of the CNI configuration file provided in json format.

* Change CNI version (0.1.0->0.3.1) of Contiv to be compatible with Multus

roles/network_plugin/multus/templates/multus-daemonset.yml.j2

@@ -0,0 +1,54 @@
+---
+kind: DaemonSet
+apiVersion: extensions/v1beta1
+metadata:
+  name: kube-multus-ds-amd64
+  namespace: kube-system
+  labels:
+    tier: node
+    app: multus
+spec:
+  template:
+    metadata:
+      labels:
+        tier: node
+        app: multus
+    spec:
+      hostNetwork: true
+      nodeSelector:
+        beta.kubernetes.io/arch: amd64
+      tolerations:
+      - key: node-role.kubernetes.io/master
+        operator: Exists
+        effect: NoSchedule
+      serviceAccountName: multus
+      containers:
+      - name: kube-multus
+        image: {{ multus_image_repo }}:{{ multus_image_tag }}
+        command: ["/entrypoint.sh"]
+        args:
+        - "--cni-conf-dir={{ multus_cni_conf_dir }}"
+        - "--cni-bin-dir={{ multus_cni_bin_dir }}"
+        - "--multus-conf-file={{ multus_conf_file }}"
+        - "--multus-kubeconfig-file-host={{ multus_kubeconfig_file_host }}"
+        resources:
+          requests:
+            cpu: "100m"
+            memory: "50Mi"
+          limits:
+            cpu: "100m"
+            memory: "50Mi"
+        securityContext:
+          privileged: true
+        volumeMounts:
+        - name: cni
+          mountPath: {{  multus_cni_conf_dir }}
+        - name: cnibin
+          mountPath: {{ multus_cni_bin_dir }}
+      volumes:
+      - name: cni
+        hostPath:
+          path: {{ multus_cni_conf_dir_host }}
+      - name: cnibin
+        hostPath:
+          path: {{ multus_cni_bin_dir_host }}