ref(contrib/linode): use cloud-config's disco-url

Author: mboersma

contrib/linode/apply-firewall.py

@@ -46,8 +46,7 @@ def get_discovery_url_from_user_data():
     try:
         current_dir = os.path.dirname(__file__)
         user_data_file = file(os.path.abspath(os.path.join(current_dir, name)), 'r')
-        user_data = yaml.safe_load(user_data_file)
-        return user_data['coreos']['etcd2']['discovery']
+        return re.search('--discovery (http\S+)', user_data_file.read()).group(1)
     except:
         raise IOError('Could not load discovery url from ' + name)