CI: Fix aarch64 publish jobs on x86

Change-Id: I5c69d288a427d708b42deadac872a3a7368181e3

.zuul.d/base.yaml

@@ -139,6 +139,7 @@
       - ^LICENSE$
       - ^tox\.ini$
     vars:
+      base_arch: "x86_64"
       publisher: false
       container_engine: "docker"
     extra-vars:

tests/playbooks/run.yml

@@ -3,14 +3,14 @@
   vars_files:
     - ../vars/zuul.yml
   vars:
-    tag_suffix: "{{ '-aarch64' if ansible_architecture == 'aarch64' else '' }}"
+    tag_suffix: "{{ '-aarch64' if base_arch == 'aarch64' else '' }}"
     kolla_build_config:
       DEFAULT:
         debug: true
         logs_dir: "{{ kolla_build_logs_dir }}"
         quiet: true
         base: "{{ base_distro }}"
-        base_arch: "{{ base_arch | default('x86_64') }}"
+        base_arch: "{{ base_arch }}"
         engine: "{{ container_engine }}"
         template_override: /etc/kolla/template_overrides.j2
         # NOTE(yoctozepto): to avoid issues with IPv6 not enabled in the docker daemon