Fix stable/train testing with tempest 26.1.0

Tis issue came up before also during we cap the Tempest
version for stable branch tests(the one moved to EM state).

Tempest use the tox constraints file while creating the tempest
virtual env in devstack/lib/tempest, installing the tempest
plugins and running the tests like in run-tempest ansible roles.
If anywhere tox constraints file is used differently then venv
will be recreated and installed tempest plugins will be gone from
that recreated venv so tempest will not be able to run the plugins
tests and fail job.

Current failure: https://aca43ed1a01d95dea0ee-dcdb6cbb330bdac08ffee1284f86c919.ssl.cf2.rackcdn.com/822225/3/check/octavia-v2-dsvm-scenario/f60e4d3/job-output.txt

Earlier I tried to fix it in a generic way by fetching the devstack
localrc - https://review.opendev.org/c/openstack/tempest/+/774913
but this solution does not seems working as we can see it is skipped
in current stable/train testing with tempest 26.1.0

Adding stable/train explicitly in list for using the stable constraint
in run-tempest role also which will be in sync with what devstack/lib/tempest
use. And later I will debug why generic way is not working.

Because of Tempest 26.1.0 and with stestr 2.5.1 (beacause of upper
constraints of stestr 2.5.1 in stable/train) which does not have
new args exclude-regex so let's fallback to old arg if new arg is passed.

Depends-On: https://review.opendev.org/c/openstack/devstack/+/822380
Depends-On: https://review.opendev.org/c/openstack/cinder-tempest-plugin/+/825708

Closes-Bug: #1955418
Change-Id: I105c839c38adfba1f9e22123ec3a99ffc0b5b72e

roles/run-tempest/README.rst

@@ -81,7 +81,7 @@ variable (through the `register` statement).
 .. zuul:rolevar:: stable_constraints_file
    :default: ''
 
-   Upper constraints file to be used for stable branch till stable/stein.
+   Upper constraints file to be used for stable branch till stable/train.
 
 .. zuul:rolevar:: tempest_tox_environment
    :default: ''

roles/run-tempest/tasks/main.yaml

@@ -25,11 +25,11 @@
     target_branch: "{{ zuul.override_checkout }}"
   when: zuul.override_checkout is defined
 
-- name: Use stable branch upper-constraints till stable/stein
+- name: Use stable branch upper-constraints till stable/train
   set_fact:
     # 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", "stable/stein"]
+  when: target_branch in ["stable/ocata", "stable/pike", "stable/queens", "stable/rocky", "stable/stein", "stable/train"]
 
 - name: Use Configured upper-constraints for non-master Tempest
   set_fact:
@@ -78,6 +78,17 @@
         exclude_list_option: "--exclude-list={{ tempest_test_exclude_list|quote }}"
       when: exclude_list_stat.stat.exists
 
+- name: stable/train workaround to fallback exclude-list to blacklist
+  # NOTE(gmann): stable/train use Tempest 26.1.0 and with stestr 2.5.1
+  # (beacause of upper constraints of stestr 2.5.1 in stable/train) which
+  # does not have new args exclude-list so let's fallback to old arg
+  # if new arg is passed.
+  set_fact:
+    exclude_list_option: "--blacklist-file={{ tempest_test_exclude_list|quote }}"
+  when:
+    - tempest_test_exclude_list is defined
+    - target_branch == "stable/train"
+
 # TODO(kopecmartin) remove this after all consumers of the role have switched
 # to tempest_exclude_regex option, until then it's kept here for the backward
 # compatibility
@@ -94,6 +105,19 @@
   when:
     - tempest_black_regex is not defined
     - tempest_exclude_regex is defined
+    - target_branch != "stable/train"
+
+- name: stable/train workaround to fallback exclude-regex to black-regex
+  # NOTE(gmann): stable/train use Tempest 26.1.0 and with stestr 2.5.1
+  # (beacause of upper constraints of stestr 2.5.1 in stable/train) which
+  # does not have new args exclude-regex so let's fallback to old arg
+  # if new arg is passed.
+  set_fact:
+    tempest_test_exclude_regex: "--black-regex={{tempest_exclude_regex|quote}}"
+  when:
+    - tempest_black_regex is not defined
+    - tempest_exclude_regex is defined
+    - target_branch == "stable/train"
 
 - name: Run Tempest
   command: tox -e {{tox_envlist}} {{tox_extra_args}} -- {{tempest_test_regex|quote}} \