[fix] Stop readline on success

Previous code was blocking on stdout after subprocess completed with
success, as `poll()` would return 0, and `not 0` is true.

chi-appliance.py

@@ -190,7 +190,7 @@ def do_configure(argv):
                                 universal_newlines=True)
         while True:
             err = proc.poll()
-            if not err:
+            if err is None:
                 print(proc.stdout.readline(), end='', flush=True)
             else:
                 if err == 0: