arc_util: properly escape unicode error message

BUG=None
TEST=None

Change-Id: I5876ffc8aba9e36c6a0cd5d26761c9d465058dc8
Reviewed-on: https://chromium-review.googlesource.com/1179425
Commit-Ready: Kuang-che Wu <kcwu@chromium.org>
Tested-by: Kuang-che Wu <kcwu@chromium.org>
Reviewed-by: Hirokazu Honda <hiroh@chromium.org>
diff --git a/client/common_lib/cros/arc_util.py b/client/common_lib/cros/arc_util.py
index f73f5ee..f143177 100644
--- a/client/common_lib/cros/arc_util.py
+++ b/client/common_lib/cros/arc_util.py
@@ -265,9 +265,9 @@
         """
         err_msg = extension_main_page.EvaluateJavaScript(js_read_error_message)
         err_msg = err_msg.strip()
-        logging.error('Error: %r', err_msg.encode('utf8'))
+        logging.error('Error: %r', err_msg)
         if err_msg:
-            raise error.TestFail('Opt-in app error: %s' % err_msg)
+            raise error.TestFail('Opt-in app error: %r' % err_msg)
         else:
             raise error.TestFail('Opt-in app did not finish running after %s '
                                  'seconds!' % SIGN_IN_TIMEOUT)