Vagrantfile: use Ubuntu 16.04 LTS
Vagrantfile: use Ubuntu 16.04 LTS

Use recent supported version of Ubuntu for local development setup
with Vagrant.

insequent/kargo,kubernetes-incubator/kubespray,kubernetes-incubator/kubespray,VincentS/kargo,galthaus/setup-kubernetes,galthaus/setup-kubernetes,sgm-media/kargo,kubernetes-sigs/kubespray,Abdelsalam-Abbas/kubespray_fork,hatch-k8s/kargo,Lendico/kargo,Atoms/kubespray,kubespray/kargo,VincentS/kargo,Abdelsalam-Abbas/kubespray_fork,Atoms/kubespray,ayaz/kubespray,Atoms/kubespray,hatch-k8s/kargo,kubernetes-sigs/kubespray,rogerwelin/kargo,rogerwelin/kargo,Lendico/kargo,kubernetes-incubator/kargo,Atoms/kubespray,kubespray/kargo,kubernetes-incubator/kargo,insequent/kargo,kubernetes-sigs/kubespray,kubernetes-sigs/kubespray,sgm-media/kargo,ayaz/kubespray