pbs: promises redirect ssh output to /dev/null

slapos/recipe/pbs.py

@@ -40,9 +40,11 @@ from slapos.recipe.librecipe import shlex
 
 
 def promise(args):
+  # Redirect output to /dev/null
+  with open("/dev/null") as _dev_null:
     ssh = subprocess.Popen(
         [args['ssh_client'], '%(user)s@%(host)s' % args, '-p', '%(port)s' % args],
-      stdin=subprocess.PIPE, stdout=None, stderr=None
+        stdin=subprocess.PIPE, stdout=_dev_null, stderr=_dev_null
     )
 
   # Rdiff Backup protocol quit command