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/download/defaults/main.yml

@@ -59,6 +59,7 @@ pod_infra_version: 3.1
 contiv_version: 1.2.1
 cilium_version: "v1.3.0"
 kube_router_version: "v0.2.1"
+multus_version: "v3.1.autoconf"
 
 # Download URLs
 kubeadm_download_url: "https://storage.googleapis.com/kubernetes-release/release/{{ kubeadm_version }}/bin/linux/{{ image_arch }}/kubeadm"
@@ -160,6 +161,8 @@ cilium_image_repo: "docker.io/cilium/cilium"
 cilium_image_tag: "{{ cilium_version }}"
 kube_router_image_repo: "cloudnativelabs/kube-router"
 kube_router_image_tag: "{{ kube_router_version }}"
+multus_image_repo: "docker.io/nfvpe/multus"
+multus_image_tag: "{{ multus_version }}"
 nginx_image_repo: nginx
 nginx_image_tag: 1.13
 dnsmasq_version: 2.78
@@ -290,6 +293,15 @@ downloads:
     groups:
       - k8s-cluster
 
+  multus:
+    enabled: "{{ kube_network_plugin_multus }}"
+    container: true
+    repo: "{{ multus_image_repo }}"
+    tag: "{{ multus_image_tag }}"
+    sha256: "{{ multus_digest_checksum|default(None) }}"
+    groups:
+      - k8s-cluster
+
   flannel:
     enabled: "{{ kube_network_plugin == 'flannel' or kube_network_plugin == 'canal' }}"
     container: true