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: I6770787e481e1eb274a8e7764aa55758d44dc9ea

openstack/mistral-extra,openstack/mistral-extra