Stable branches till stable/rocky is using python
version <py3.6. Tempest test those branch in venv
but Tempest tox use the master upper-constraint
which block installation due to dependencies
require >=py3.6. For exmaple, oslo.concurrency 4.0.0
is not compatible for <py3.6.
As we pin Tempest for EM stable brach, we should be
able to use stable constraint for Tempest installation
as well as while running during run-tempest playbook.
tox.ini is hard coded to use master constraint which force
legacy ocata job to use the master constraints and fail
Devstack can set stable u-c to use via env var but this is
not enough as Tempest recreate the tox env with master u-c
when run test via devstack-gate.
All other branches have been fixed by fixing the run-tempest playbooks
in same way.
Because stable/ocata and grenade job use devstack-gate, we need to fix this.
This is required to fix the grenade jobs on each stable branch to
get the other fixes in.