tests: fix checks when the locale is not the default one

Some tests (test_pbutils.py) checks against strings for the
english locale, so we should force it before running any test

https://bugzilla.gnome.org/show_bug.cgi?id=640207

testsuite/runtests.py

@@ -28,6 +28,8 @@ import unittest
 
 SKIP_FILES = ['common', 'runtests']
 
+os.environ['LC_MESSAGES'] = 'C'
+
 def gettestnames(which):
     if not which:
         dir = os.path.split(os.path.abspath(__file__))[0]