Bug 829664 - `make check` fails on mozbuild/test/test_mozconfig.py with MOZCONFIG set;r=gps

--HG--
extra : rebase_source : 528f17303eaf11fe92f430c79b21a410aac50251

python/mozbuild/mozbuild/test/test_mozconfig.py

@@ -28,6 +28,7 @@ from mozbuild.mozconfig import (
 class TestMozconfigLoader(unittest.TestCase):
     def setUp(self):
         self._old_env = dict(os.environ)
+        os.environ.pop('MOZCONFIG', None)
         self._temp_dirs = set()
 
     def tearDown(self):