Add Vagrant CI for Ubuntu 20.04 (#6279)

tests/files/vagrant_ubuntu20-flannel.rb

@@ -0,0 +1,9 @@
+$os = "ubuntu2004"
+
+# For CI we are not worries about data persistence across reboot
+$libvirt_volume_cache = "unsafe"
+
+# Checking for box update can trigger API rate limiting
+# https://www.vagrantup.com/docs/vagrant-cloud/request-limits.html
+$box_check_update = false
+$vm_cpus = 2

tests/files/vagrant_ubuntu20-flannel.yml

@@ -0,0 +1,7 @@
+---
+# Kubespray settings
+
+kube_network_plugin: flannel
+
+deploy_netchecker: true
+dns_min_replicas: 1