Use deprecated s3 mock from moto.

Longer term we should move to boto3 in general and then we can use the
default moto mock for s3.

common/test/utils.py

@@ -124,7 +124,7 @@ class MockS3Mixin(object):
     """
     def setUp(self):
         super(MockS3Mixin, self).setUp()
-        self._mock_s3 = moto.mock_s3()
+        self._mock_s3 = moto.mock_s3_deprecated()
         self._mock_s3.start()
 
     def tearDown(self):

lms/djangoapps/verify_student/tests/test_views.py

@@ -1489,7 +1489,7 @@ class TestSubmitPhotosForVerification(TestCase):
         "DAYS_GOOD_FOR": 10,
     })
     @httpretty.activate
-    @moto.mock_s3
+    @moto.mock_s3_deprecated
     def test_submit_photos_for_reverification(self):
         # Create the S3 bucket for photo upload
         conn = boto.connect_s3()