Fix setting etcd client cert serial (#1775)

roles/etcd/tasks/main.yml

@@ -15,7 +15,12 @@
 
 - name: "Gen_certs | Get etcd certificate serials"
   shell: "openssl x509 -in {{ etcd_cert_dir }}/node-{{ inventory_hostname }}.pem -noout -serial | cut -d= -f2"
-  register: "etcd_client_cert_serial"
+  register: "etcd_client_cert_serial_result"
+  when: inventory_hostname in groups['k8s-cluster']|union(groups['etcd'])|union(groups['calico-rr']|default([]))|unique|sort
+
+- name: Set etcd_client_cert_serial
+  set_fact:
+    etcd_client_cert_serial: "{{ etcd_client_cert_serial_result.stdout }}"
   when: inventory_hostname in groups['k8s-cluster']|union(groups['etcd'])|union(groups['calico-rr']|default([]))|unique|sort
 
 - include: "install_{{ etcd_deployment_type }}.yml"