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.
Add missing dev packages for libxml and libxslt to the bindep config
for more details.
Signed-off-by: Doug Hellmann <email@example.com>
Those are not installed anymore by default and are needed to fix builds
of python modules.
Add bindep.txt file with packages needed to use the repository.