use test -f instead of ls

apache/vhosts/standard.sls

@@ -24,7 +24,7 @@ include:
 a2ensite {{ id }}:
   cmd:
     - run
-    - unless: ls /etc/apache2/sites-enabled/{{ id }}
+    - unless: test -f /etc/apache2/sites-enabled/{{ id }}
     - require:
       - file: {{ id }}
     - watch_in: