Be able to know when we are running inside a minor update workflow

With this change we add an ansible variable called
'tripleo_minor_update' set to true only during the update_steps_playbook
which get run during a minor update.
Then inside common/deploy-steps-tasks when starting containers with
paunch we export this 'tripleo_minor_update' ansible variable and
push it inside the 'TRIPLEO_MINOR_UPDATE' environment variable.

Inside change Id1d671506d3ec827bc311b47d9363952e1239ce3 we will then
use the env variable and export it to the restart_bundles in order
to detect if we're inside a minor update workflow (as opposed to
a redeploy - aka stack update). The testing that has been done is
described in the above change.

Co-Authored-By: Damien Ciabrini <dciabrin@redhat.com>

Change-Id: Ib3562adbd83f7162c2aeb450329b7cc4ab200fc2

common/deploy-steps-tasks.yaml

@@ -470,6 +470,8 @@
     # we have new paunch version related to
     # https://review.openstack.org/#/c/635438/
     - name: Start containers for step {{ step }}
+      environment:
+        TRIPLEO_MINOR_UPDATE: '{{ tripleo_minor_update | default(false) }}'
       command: >-
         paunch {% if enable_debug|bool %}--debug{% else %}-v{% endif %} apply
         --default-runtime "{{ container_cli }}"

common/deploy-steps.j2

@@ -504,6 +504,7 @@ outputs:
                 docker_puppet_debug: DOCKER_PUPPET_DEBUG
                 docker_puppet_process_count: DOCKER_PUPPET_PROCESS_COUNT
                 docker_puppet_mount_host_puppet: DOCKER_PUPPET_MOUNT_HOST_PUPPET
+                tripleo_minor_update: true
               tasks:
                 - include_tasks: update_steps_tasks.yaml
                   with_sequence: start=0 end={{update_steps_max-1}}

releasenotes/notes/minor-update-env-20657417094d4aeb.yaml

@@ -0,0 +1,7 @@
+---
+fixes:
+  - |
+    It is now possible for temporary containers inside THT to test if they are being run
+    as part of a minor update by checking if the TRIPLEO_MINOR_UPDATE environment
+    variable is set to 'true' (said containers need to export it to the container explicitely),
+    see <service>_restart_bundles for examples.