python 3 support in zanata_stats.py
python 3 support in zanata_stats.py

* requests library handles differences in Python 2 and 3 efficiently.
  Let's switch to requests rather than using the lower-level urllib.
* CSV writer in Python3 expects a file is open as
  non-binary mode. In Python 2, binary mode is expected.

Change-Id: Ied870913de54975ea2d734e719f05c1e342620eb

openstack/i18n,openstack/i18n