bisect-kit: fix lint warnings from new lint rules

This also improved python3 compatibility.

BUG=b:140004822
TEST=pylint; unittest

Change-Id: I487e25a055190dd5d4059e8a0c0589170c182dea
diff --git a/bisect_kit/android_util.py b/bisect_kit/android_util.py
index 3f6f697..559143f 100644
--- a/bisect_kit/android_util.py
+++ b/bisect_kit/android_util.py
@@ -60,10 +60,10 @@
   # Following code is just serving as demo purpose. You should modify or hook
   # it with your own implementation.
   logger.warn('fetch_android_build_data need to be hooked')
-  import urllib2
+  from six.moves import urllib
   try:
-    return urllib2.urlopen(url).read()
-  except urllib2.URLError as e:
+    return urllib.request.urlopen(url).read()
+  except urllib.request.URLError as e:
     logger.exception('failed to fetch "%s"', url)
     raise errors.ExternalError(str(e))