Fixed branch matching for parent jobs when on stable/1.0.0 branch

When a patch is submitted against a branch, Zuul CI will collect job
variants for each ci job and all its parent jobs. If both job.\
override-checkout and job.required-projects.override-checkout
attributes are not defined, then Zuul will for each (parent) job match
the current branch of the patch against all branches of the project in
which the job is defined. If no such branch exist in a project, then no
job variant matches and this job will be ignored [1].
For example, if a patch is submitted for our stable/1.0.0 branch, then
Zuul CI will try to match 'stable/1.0.0' against all branches in the
projects where job ansible-collections-openstack-functional-devstack
and its parent job openstacksdk-functional-devstack are defined. The
first is defined in openstack/ansible-collections-openstack/.zuul.yaml,
so a match for stable/1.0.0 will be found. But openstacksdk-functional-\
devstack is defined in openstack/openstacksdk/.zuul.yaml which has no
branch stable/1.0.0 defined. So Zuul will not schedule job ansible-\
collections-openstack-functional-devstack at all.

The solution is twofold. First, the base jobs such as ansible-\
collections-openstack-functional-devstack have to be changed to always
checkout existing branches in projects which define (parent) jobs.
Using job.override-checkout might have unintended sideeffects because
it will checkout the specified branch for all required projects which
also includes the project which the patch was submitted for. Instead
we set job.required-projects.override-checkout for all projects which
define parent jobs. For example, in ansible-collections-openstack-\
functional-devstack we set job.required-projects.override-checkout to
master for opendev.org/openstack/devstack which defines parent job
openstack-functional-devstack.

In child jobs which (re)define job.override-checkout, we have to change
job.required-projects.override-checkout for all projects which define
parent jobs to the value of job.override-checkout. If we fail to update
job.required-projects.override-checkout then Zuul will checkout the
branch which was defined in the base jobs because job.\
required-projects.override-checkout has higher precedence than job.\
override-checkout.

Setting attribute project.<pipeline>.debug to true helps with debugging
these job scheduling issues. "If this is set to true, Zuul will include
debugging information in reports it makes about items in the pipeline.
This should not normally be set, but in situations were it is difficult
to determine why Zuul did or did not run a certain job, the additional
information this provides may help" [2].

Note, once job scheduling has been completed, Zuul will use a different
algorithm to checkout projects which are listed in job.\
required-projects [3][4]. It will fallback to a default branch if no
matching branch can be found in projects [5].

Ref.:
[1] https://opendev.org/zuul/zuul/src/branch/master/zuul/model.py#L6996
[2] https://zuul-ci.org/docs/zuul/latest/config/project.html#attr-project.%3Cpipeline%3E.debug
[3] https://zuul-ci.org/docs/zuul/latest/job-content.html#git-repositories
[4] https://opendev.org/zuul/zuul/src/branch/master/zuul/executor/server.py#L1648
[5] https://zuul-ci.org/docs/zuul/latest/config/project.html#attr-project.default-branch

Change-Id: I31f9607ab7e2e2ae8534429da7f5e5f235560c56

.zuul.yaml

@@ -11,6 +11,13 @@
     required-projects:
       - openstack/ansible-collections-openstack
       - openstack/designate
+      # openstack/os-client-config is required through job openstacksdk-functional-devstack
+      - # always use master branch when collecting parent job variants, refer to git blame for rationale.
+        name: openstack/devstack
+        override-checkout: master
+      - # always use master branch when collecting parent job variants, refer to git blame for rationale.
+        name: openstack/openstacksdk
+        override-checkout: master
     irrelevant-files: &ignore_files
       - changelogs/.*
       - galaxy.*
@@ -146,7 +153,10 @@
       using xena branch of openstacksdk and stable 2.12 branch of ansible
     branches: stable/1.0.0
     override-checkout: stable/xena
+    # job.override-checkout will not override job.required-projects.override-checkout in parent jobs
     required-projects:
+      - name: openstack/devstack
+        override-checkout: stable/xena
       - name: openstack/openstacksdk
         override-checkout: stable/xena
 
@@ -158,7 +168,10 @@
       using wallaby branch of openstacksdk and stable 2.12 branch of ansible
     branches: stable/1.0.0
     override-checkout: stable/wallaby
+    # job.override-checkout will not override job.required-projects.override-checkout in parent jobs
     required-projects:
+      - name: openstack/devstack
+        override-checkout: stable/wallaby
       - name: openstack/openstacksdk
         override-checkout: stable/wallaby
 
@@ -170,7 +183,10 @@
       using victoria branch of openstacksdk and stable 2.12 branch of ansible
     branches: stable/1.0.0
     override-checkout: stable/victoria
+    # job.override-checkout will not override job.required-projects.override-checkout in parent jobs
     required-projects:
+      - name: openstack/devstack
+        override-checkout: stable/victoria
       - name: openstack/openstacksdk
         override-checkout: stable/victoria
 
@@ -182,10 +198,11 @@
       using ussuri branch of openstacksdk and stable 2.11 branch of ansible
     branches: stable/1.0.0
     override-checkout: stable/ussuri
+    # job.override-checkout will not override job.required-projects.override-checkout in parent jobs
     required-projects:
-      - name: openstack/openstacksdk
+      - name: openstack/devstack
         override-checkout: stable/ussuri
-      - name: openstack/os-client-config
+      - name: openstack/openstacksdk
         override-checkout: stable/ussuri
 
 - job:
@@ -196,10 +213,11 @@
       using train branch of openstacksdk and stable 2.11 branch of ansible
     branches: stable/1.0.0
     override-checkout: stable/train
+    # job.override-checkout will not override job.required-projects.override-checkout in parent jobs
     required-projects:
-      - name: openstack/openstacksdk
+      - name: openstack/devstack
         override-checkout: stable/train
-      - name: openstack/os-client-config
+      - name: openstack/openstacksdk
         override-checkout: stable/train
 
 - job:
@@ -210,7 +228,10 @@
       using train branch of openstacksdk and stable 2.11 branch of ansible
     branches: stable/1.0.0
     override-checkout: stable/queens
+    # job.override-checkout will not override job.required-projects.override-checkout in parent jobs
     required-projects:
+      - name: openstack/devstack
+        override-checkout: stable/queens
       - name: openstack/openstacksdk
         # Run queens with highest possible py2 version of SDK
         override-checkout: stable/train
@@ -264,12 +285,17 @@
     parent: bifrost-integration-tinyipa-ubuntu-focal
     required-projects:
       - openstack/ansible-collections-openstack
-
+      - # always use master branch when collecting parent job variants, refer to git blame for rationale.
+        name: openstack/bifrost
+        override-checkout: master
 - job:
     name: bifrost-keystone-collections-src
     parent: bifrost-integration-tinyipa-keystone-ubuntu-focal
     required-projects:
       - openstack/ansible-collections-openstack
+      - # always use master branch when collecting parent job variants, refer to git blame for rationale.
+        name: openstack/bifrost
+        override-checkout: master
 
 # TripleO jobs
 - job:
@@ -279,6 +305,11 @@
       featureset: '052'
       consumer_job: false
       build_container_images: true
+    required-projects:
+      - openstack/ansible-collections-openstack
+      - # always use master branch when collecting parent job variants, refer to git blame for rationale.
+        name: openstack/tripleo-ci
+        override-checkout: master
     irrelevant-files: &irr_files
       - .*molecule.*
       - ^.*\.md$