set default value of name to "k8s-pod-network" (#8813)

Signed-off-by: cyclinder <qifeng.guo@daocloud.io>

inventory/sample/group_vars/k8s_cluster/k8s-net-calico.yml

+---
 # see roles/network_plugin/calico/defaults/main.yml
 
+# the default value of name
+calico_cni_name: k8s-pod-network
+
 ## With calico it is possible to distributed routes with border routers of the datacenter.
 ## Warning : enabling router peering will disable calico's default behavior ('node mesh').
 ## The subnets of each nodes will be distributed by the datacenter router

roles/network_plugin/calico/defaults/main.yml

 ---
+# the default value of name
+calico_cni_name: k8s-pod-network
+
 # Enables Internet connectivity from containers
 nat_outgoing: true
 

roles/network_plugin/calico/templates/cni-calico.conflist.j2

 {
-  "name": "cni0",
+  "name": "{{ calico_cni_name }}",
   "cniVersion":"0.3.1",
   "plugins":[
     {