adds missing serialize_instance function

lib/ansible/modules/extras/cloud/vmware/vca_nat.py

@@ -145,6 +145,12 @@ LOGIN_HOST['vca']     = 'vca.vmware.com'
 LOGIN_HOST['vchs']    = 'vchs.vmware.com'
 VALID_RULE_KEYS       = ['rule_type', 'original_ip', 'original_port', 'translated_ip', 'translated_port', 'protocol']
 
+def serialize_instances(instance_list):
+    instances = []
+    for i in instance_list:
+        instances.append(dict(apiUrl=i['apiUrl'], instance_id=i['id']))
+    return instances
+
 def vca_login(module=None):
     service_type    = module.params.get('service_type')
     username        = module.params.get('username')