Fix NPTest.pm not asking for unconfigured variables

It appeats STDERR isn't a tty anymore during tests, but since we type
from tty to STDIN it should be bound to our tty (and works for me).

NPTest.pm

@@ -347,7 +347,7 @@ sub getTestParameter
   }
 
   # Set "none" if no terminal attached (eg, tinderbox build servers when new variables set)
-  return "" unless (-t STDERR);
+  return "" unless (-t STDIN);
 
   my $userResponse = "";