fixed missing metadata property

This property needs to be set to 'yes' or else cloud-init based templates won't work

Author: tvarsis

upcloud_api/server.py

@@ -325,6 +325,7 @@ def prepare_post_body(self):
             'hostname': self.hostname,
             'zone': self.zone,
             'title': self.title,
+            'metadata': self.metadata,
             'storage_devices': {},
         }