* Add a network_mtu input variable (default 1500)
* Set the Calico CNI config (i.e. workload network interfaces)
* Set the Calico IP in IP MTU (for tunnel network interfaces)
* Add support for using Calico pod networking instead of flannel
* Add variable "networking" which may be "calico" or "flannel"
* Users MUST move the contents of assets_dir/manifests-networking
into the assets_dir/manifests directory before running bootkube
start. This is needed because Terraform cannot generate conditional
files into a template_dir because other resources write to the same
directory and delete.
https://github.com/terraform-providers/terraform-provider-template/issues/10