only use unicodecsv for python 2.x

Only use unicodecsv for python 2, since the python 3 module works fine
with unicode data.

Change-Id: I8b82248e855a6986b7541ca997d8fd56628b17a5
Related-bug: #1491888

cliff/formatters/commaseparated.py

@@ -1,7 +1,11 @@
 """Output formatters using csv format.
 """
 
-import unicodecsv as csv
+import sys
+if sys.version_info[0] == 3:
+    import csv
+else:
+    import unicodecsv as csv
 import os
 
 from .base import ListFormatter

requirements.txt

@@ -8,5 +8,5 @@ PrettyTable<0.8,>=0.7
 pyparsing>=2.0.1
 six>=1.9.0
 stevedore>=1.5.0 # Apache-2.0
-unicodecsv>=0.8.0
+unicodecsv>=0.8.0;python_version=='2.7' or python_version=='2.6'
 PyYAML>=3.1.0