Set TOX_CONSTRAINTS_FILE

UPPER_CONSTRAINTS_FILE is deprecatedi[1], set the newer
TOX_CONSTRAINTS_FILE as well when interacting with other repos for the
transition.

Update internal use but not the tox.ini file, since users calling it
might use the old variable.

[1] https://zuul-ci.org/docs/zuul-jobs/python-roles.html#rolevar-tox.tox_constraints_file

Change-Id: Iea09402cf918a6978120a341950643185c94ec85
diff --git a/roles/run-tempest/tasks/main.yaml b/roles/run-tempest/tasks/main.yaml
index 8686f9a..82bc265 100644
--- a/roles/run-tempest/tasks/main.yaml
+++ b/roles/run-tempest/tasks/main.yaml
@@ -27,7 +27,8 @@
 
 - name: Use stable branch upper-constraints till stable/rocky
   set_fact:
-    tempest_tox_environment: "{{ tempest_tox_environment | combine({'UPPER_CONSTRAINTS_FILE': stable_constraints_file}) }}"
+    # TOX_CONSTRAINTS_FILE is new name, UPPER_CONSTRAINTS_FILE is old one, best to set both
+    tempest_tox_environment: "{{ tempest_tox_environment | combine({'UPPER_CONSTRAINTS_FILE': stable_constraints_file}) | combine({'TOX_CONSTRAINTS_FILE': stable_constraints_file}) }}"
   when: target_branch in ["stable/ocata", "stable/pike", "stable/queens", "stable/rocky"]
 
 - name: Set OS_TEST_TIMEOUT if requested