[LIBCLOUD-638] Can't set CORS headers via container.upload_object_via_stream()

https://issues.apache.org/jira/browse/LIBCLOUD-638
You can replace `import unittest` with from `libcloud.test import unittest`.

This way it will use stdlib `unittest` library with Python >= 2.7 and unittest2 with Python < 2.7 which means you can then use assertDictEqual.