fix scaling in kubeadm etcd mode (#6822)

'ansible.vars.hostvars.HostVarsVars object' has no attribute 'kubeadm_upload_cert'

kubeadm_upload_cert will never be found as a hostvar for the first
master since the task is executed for a worker.

Fix by executing the upload task for the first master and register
the needed key. After that, workers can read hostvars for the master

Var kubeadm_etcd_refresh_cert_key removed since it no longer has
any use.

scale.yml

@@ -74,6 +74,25 @@
     - { role: kubernetes/node, tags: node }
   environment: "{{ proxy_env }}"
 
+- name: Upload control plane certs and retrieve encryption key
+  hosts: kube-master | first
+  tags: kubeadm
+  tasks:
+    - name: include needed vars
+      include_vars: roles/kubespray-defaults/defaults/main.yaml
+    - name: Upload control plane certificates
+      command: >-
+        {{ bin_dir }}/kubeadm init phase
+        --config {{ kube_config_dir }}/kubeadm-config.yaml
+        upload-certs
+        --upload-certs
+      register: kubeadm_upload_cert
+      changed_when: false
+    - name: set fact 'kubeadm_certificate_key' for later use
+      set_fact:
+        kubeadm_certificate_key: "{{ kubeadm_upload_cert.stdout_lines[-1] | trim }}"
+      when: kubeadm_certificate_key is not defined
+
 - name: Target only workers to get kubelet installed and checking in on any new nodes(network)
   hosts: kube-node
   gather_facts: False