Add Rocky Linux 8 support for vagrant (#8905)

To test Kubespray on Rocky Linux 8 with vagrant, this adds it to
the Vagrantfile.

tests/files/packet_rockylinux8-calico.yml

@@ -0,0 +1,11 @@
+---
+# Instance settings
+cloud_image: rockylinux-8
+mode: default
+vm_memory: 3072Mi
+
+# Kubespray settings
+metrics_server_enabled: true
+dashboard_namespace: "kube-dashboard"
+dashboard_enabled: true
+loadbalancer_apiserver_type: haproxy