add new clusterNetworks fields to new installs

add clusterNetworks field to the networkConfig so that the new fields
appear in new installs when openshift version is greater then 3.7

roles/openshift_master/templates/master.yaml.v1.j2

@@ -179,6 +179,11 @@ masterPublicURL: {{ openshift.master.public_api_url }}
 networkConfig:
   clusterNetworkCIDR: {{ openshift.master.sdn_cluster_network_cidr }}
   hostSubnetLength: {{ openshift.master.sdn_host_subnet_length }}
+{% if openshift.common.version_gte_3_7 | bool %}
+  clusterNetworks:
+  - cidr: {{ openshift.master.sdn_cluster_network_cidr }}
+    hostSubnetLength: {{ openshift.master.sdn_host_subnet_length }}
+{% endif %}
 {% if r_openshift_master_use_openshift_sdn or r_openshift_master_use_nuage or r_openshift_master_use_contiv or r_openshift_master_use_kuryr or r_openshift_master_sdn_network_plugin_name == 'cni' %}
   networkPluginName: {{ r_openshift_master_sdn_network_plugin_name_default }}
 {% endif %}