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

Vagrantfile

@@ -35,6 +35,8 @@ $forwarded_ports = {}
 $subnet = "172.17.8"
 $os = "ubuntu1804"
 $network_plugin = "flannel"
+# Setting multi_networking to true will install Multus: https://github.com/intel/multus-cni
+$multi_networking = false
 # The first three nodes are etcd servers
 $etcd_instances = $num_instances
 # The first two nodes are kube masters
@@ -140,7 +142,8 @@ Vagrant.configure("2") do |config|
         "ip": ip,
         "local_release_dir" => $local_release_dir,
         "download_run_once": "False",
-        "kube_network_plugin": $network_plugin
+        "kube_network_plugin": $network_plugin,
+        "kube_network_plugin_multus": $multi_networking
       }
 
       config.vm.network :private_network, ip: ip