Using tox for requirements management requires in-repo
requirements files for all our repositories. Rather than
do that, we make use of the tests repo to capture our
common requirements and use this to install them.
This reduces our review requirement rate and simplifies
maintenance for us for the tox config. It also makes it
usable with 'Depends-On', which is marvellous!
The tox requirements definitions for docs/releasenotes
builds are left in-place as those are standard entries
across the community. If that changes at some point, we
can re-assess those entries too.
Depends-On: https://review.openstack.org/579208
Change-Id: I2374264953e2ad2eb10994cdbbac6bfc20c9bec0