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/kubernetes-apps/network_plugin/meta/main.yml

@@ -34,3 +34,8 @@ dependencies:
     when: kube_network_plugin == 'kube-router'
     tags:
       - kube-router
+
+  - role: kubernetes-apps/network_plugin/multus
+    when: kube_network_plugin_multus
+    tags:
+      - multus