This commit is a workaround for respecting upper-constraints. Since
we're using tox to handle setting up a venv and running tempest
commands we need to manually install the constrained packages inside
the tox venvs. This patch does that for all the venvs being created by
devstack via tox. However, since tempest has additional tox jobs
defined if those are run via devstack those will default to the
default pip install -U -r requirements.txt defined in tempest's
tox.ini.
Change-Id: I7f84dfb67a3c97003947aefd8a7e3c6454106db4
Closes-Bug: #1543841
1e31e68557