Fix k8s-certs-renew for k8s < 1.20 (#7410)

Signed-off-by: Etienne Champetier <e.champetier@ateme.com>
(cherry picked from commit 2d1597bf10)

roles/kubernetes/master/templates/k8s-certs-renew.sh.j2

@@ -1,10 +1,10 @@
 #!/bin/bash
 
 echo "## Expiration before renewal ##"
-{{ bin_dir }}/kubeadm certs check-expiration
+{{ bin_dir }}/kubeadm {{ 'alpha ' if kube_version is version('v1.20.0', '<') }}certs check-expiration
 
 echo "## Renewing certificates managed by kubeadm ##"
-{{ bin_dir }}/kubeadm certs renew all
+{{ bin_dir }}/kubeadm {{ 'alpha ' if kube_version is version('v1.20.0', '<') }}certs renew all
 
 echo "## Restarting control plane pods managed by kubeadm ##"
 {% if container_manager == "docker" %}
@@ -20,4 +20,4 @@ echo "## Waiting for apiserver to be up again ##"
 until printf "" 2>>/dev/null >>/dev/tcp/127.0.0.1/6443; do sleep 1; done
 
 echo "## Expiration after renewal ##"
-{{ bin_dir }}/kubeadm certs check-expiration
+{{ bin_dir }}/kubeadm {{ 'alpha ' if kube_version is version('v1.20.0', '<') }}certs check-expiration