Improve python 3 compatibility for doctest.py

Fix import of urllib.
Use "print(" instead of "print ("

Change-Id: I3bc6e086c64ed8b84104e4c5bf76f46b932ceb2e

os_doc_tools/doctest.py

@@ -36,9 +36,14 @@ import operator
 import os
 import re
 import shutil
+import six
 import subprocess
 import sys
 import time
+
+if six.PY3:
+    from urllib import request as urllib2
+else:
     import urllib2
 
 from lxml import etree