According to OpenStack summit session [1], stestr is
maintained project to which all OpenStack projects should
migrate.
Let's switch to stestr as other projects have already
moved to it.
Uses environment inclusions which need tox 2.8.1 due to
a bug fix. So increase the tox minversion.
[1] https://etherpad.openstack.org/p/YVR-python-pti
Change-Id: If6eded0dd802cbdfe49ad72c64004585d4a1484b
Create a tox environment for running the unit tests
against the lower bounds of the dependencies.
Create a lower-constraints.txt to be used to enforce the
lower bounds in those tests.
Add openstack-tox-lower-constraints job to the zuul
configuration.
See [1] for details.
1. http://lists.openstack.org/pipermail/openstack-dev/2018-March/128352.html
Change-Id: I0f8b1bd44cd2f401593ce079cdecce5020807051