Rename ansible groups to use _ instead of - (#7552)

* rename ansible groups to use _ instead of -

k8s-cluster -> k8s_cluster
k8s-node -> k8s_node
calico-rr -> calico_rr
no-floating -> no_floating

Note: kube-node,k8s-cluster groups in upgrade CI
      need clean-up after v2.16 is tagged

* ensure old groups are mapped to the new ones

roles/download/tasks/prep_kubeadm_images.yml

@@ -55,7 +55,7 @@
         container: true
         repo: "{{ item | regex_replace('^(.*):.*$','\\1') }}"
         tag: "{{ item | regex_replace('^.*:(.*)$','\\1') }}"
-        groups: k8s-cluster
+        groups: k8s_cluster
   loop: "{{ kubeadm_images_list | flatten(levels=1) }}"
   register: kubeadm_images_cooked
   run_once: true