fix test if openstack_cacert is a base64 string (#6371)

roles/kubernetes/node/tasks/main.yml

@@ -189,7 +189,7 @@
 
 - name: Test if openstack_cacert is a base64 string
   set_fact:
-    openstack_cacert_is_base64: "{% if openstack_cacert | b64decode %}true{% else %}false{% endif %}"
+    openstack_cacert_is_base64: "{% if openstack_cacert | search ('^([A-Za-z0-9+/]{4})*([A-Za-z0-9+/]{3}=|[A-Za-z0-9+/]{2}==)?$') %}true{% else %}false{% endif %}"
   when:
     - cloud_provider is defined
     - cloud_provider == 'openstack'