Fix unittest issue related to python2/python3 differences

The test_datetime test passed on python3 but not python2 because
datetime.strftime is a byte string in python2, and a unicode string in python3

This patch allows the test to pass in both python2 and python3 (3.3+ only)
Merge pull request #1307 from al-tonio/datetestfix

Fix unittest issue related to python2/python3 differences