Use absolute import to import locale

Since locale folder has been created with the translations, Python3 tests
failed because 2to3 converts the import of locale into a relative import
because it detects the locale folder.

carrier.py

@@ -1,5 +1,7 @@
 # This file is part of Tryton.  The COPYRIGHT file at the top level of
 # this repository contains the full copyright notices and license terms.
+from __future__ import absolute_import
+
 import locale
 
 from zeep.exceptions import Fault

stock.py

@@ -1,5 +1,6 @@
 # This file is part of Tryton.  The COPYRIGHT file at the top level of
 # this repository contains the full copyright notices and license terms.
+from __future__ import absolute_import
 
 import locale
 from io import BytesIO