update flannel for windows

Author: nader-ziada

templates/test/ci/cluster-template-prow-custom-vnet.yaml

@@ -47,7 +47,7 @@ spec:
       securityGroup:
         name: node-nsg
     vnet:
-      name: ${AZURE_VNET_NAME}
+      name: ${AZURE_VNET_NAME:=${CLUSTER_NAME}-vnet}
   resourceGroup: ${AZURE_RESOURCE_GROUP:=${CLUSTER_NAME}}
   subscriptionID: ${AZURE_SUBSCRIPTION_ID}
 ---

templates/test/ci/prow-custom-vnet/patches/custom-vnet.yaml

@@ -5,7 +5,7 @@ metadata:
 spec:
   networkSpec:
     vnet:
-      name: ${AZURE_VNET_NAME}
+      name: ${AZURE_VNET_NAME:=${CLUSTER_NAME}-vnet}
     subnets:
       - name: ${CLUSTER_NAME}-controlplane-subnet
         role: control-plane