factory: Use six.moves.input instead of raw_input

`raw_input` is deprecated and rename to `input` in python3.

However, `input` is a builtin function in python2. Hence, we need to use
`six.moves.input` to write py2/3 compatible code.

BUG=chromium:999876
TEST=make test
TEST=make lint and check there is no raw_input-builtin error

Change-Id: Id28d1c8b095d8c456bd444ae6ddef0eb5f7ce3cc
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/factory/+/1872132
Tested-by: Yilin Yang <kerker@chromium.org>
Auto-Submit: Yilin Yang <kerker@chromium.org>
Commit-Queue: Yilin Yang <kerker@chromium.org>
Reviewed-by: Yong Hong <yhong@chromium.org>
diff --git a/py/toolkit/installer.py b/py/toolkit/installer.py
index bc5d66e..b39c24f 100755
--- a/py/toolkit/installer.py
+++ b/py/toolkit/installer.py
@@ -23,6 +23,8 @@
 import tempfile
 import time
 
+from six.moves import input
+
 import factory_common  # pylint: disable=unused-import
 from cros.factory.test.env import paths
 from cros.factory.test.test_lists import test_list_common
@@ -511,7 +513,7 @@
     print(installer.WarningMessage(args.dest if patch_test_image else None))
 
     if not args.yes:
-      answer = raw_input('*** Continue? [y/N] ')
+      answer = input('*** Continue? [y/N] ')
       if not answer or answer[0] not in 'yY':
         sys.exit('Aborting.')