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/files/multus-clusterrole.yml

@@ -0,0 +1,16 @@
+---
+kind: ClusterRole
+apiVersion: rbac.authorization.k8s.io/v1beta1
+metadata:
+  name: multus
+rules:
+- apiGroups:
+  - '*'
+  resources:
+  - '*'
+  verbs:
+  - '*'
+- nonResourceURLs:
+  - '*'
+  verbs:
+  - '*'