Make calico interface configurable

This is useful in environments with multiple interfaces.  It is even
useful in the example Vagrant environment.

example/vagrant-input-config.yaml

@@ -8,6 +8,7 @@ spec:
   nodes:
     n0:
       ip: 192.168.77.10
+      kubernetes_interface: enp0s8
       roles:
         - master
         - genesis
@@ -15,18 +16,21 @@ spec:
         - beta.kubernetes.io/arch=amd64
     n1:
       ip: 192.168.77.11
+      kubernetes_interface: enp0s8
       roles:
         - master
       additional_labels:
         - beta.kubernetes.io/arch=amd64
     n2:
       ip: 192.168.77.12
+      kubernetes_interface: enp0s8
       roles:
         - master
       additional_labels:
         - beta.kubernetes.io/arch=amd64
     n3:
       ip: 192.168.77.13
+      kubernetes_interface: enp0s8
       roles:
         - worker
       additional_labels:

promenade/templates/genesis/etc/kubernetes/asset-loader/cni/calico.yaml

@@ -187,6 +187,10 @@ spec:
             # Auto-detect the BGP IP address.
             - name: IP
               value: ""
+            {%- if config['Node']['kubernetes_interface'] is defined %}
+            - name: IP_AUTODETECTION_METHOD
+              value: interface={{ config['Node']['kubernetes_interface'] }}
+            {%- endif %}
           securityContext:
             privileged: true
           resources: