Add the restructuredtext check to the flake8 job
Add the restructuredtext check to the flake8 job

This follows a recommendation in this thread on openstack-dev.
http://lists.openstack.org/pipermail/openstack-dev/2018-June/131233.html

Change-Id: Idaf7b80657918681b25c154f5a81b0a515c82b52

openstack/python-mistralclient,openstack/python-mistralclient