calico: avoid POD restart during initial deploy (kubernetes-sigs#6886)

calico PODs are first started and then in a handler killed and
restarted for no reason, nothing has changed.

By using the existing variable 'calico_cni_config' (only defined when
calico has already started) the restart can be skipped.

roles/network_plugin/calico/handlers/main.yml

@@ -1,6 +1,7 @@
 ---
 - name: reset_calico_cni
   command: /bin/true
+  when: calico_cni_config is defined
   notify:
     - delete 10-calico.conflist
     - docker | delete calico-node containers