tests: drop use of 'unittest2' (#1564)

diff --git a/tests/test_http.py b/tests/test_http.py
index 5484269..852cd7e 100644
--- a/tests/test_http.py
+++ b/tests/test_http.py
@@ -31,7 +31,7 @@
 import logging
 import mock
 import os
-import unittest2 as unittest
+import unittest
 import urllib
 import random
 import socket