Move containerfile setting in container build

When setting the containerfile variable, we need to be inside the
zk_images loop in order to set the correct default for each image.

Change-Id: I216ffd19dd797752b2e5ca2332e651b8e6ac8a3c

roles/build-container-image/tasks/build.yaml

@@ -1,3 +1,7 @@
+- name: Set container filename arg
+  set_fact:
+    containerfile: "{{ zj_image.container_filename | default(container_filename) | default('') }}"
+
 - name: Set up siblings
   include_tasks: siblings.yaml
 

roles/build-container-image/tasks/buildx.yaml

@@ -8,6 +8,10 @@
   set_fact:
     _repopath: "{{ (zj_image.repository | split('/', 1)).1 }}"
 
+- name: Set container filename arg
+  set_fact:
+    containerfile: "{{ zj_image.container_filename | default(container_filename) | default('') }}"
+
 - name: Set up siblings
   include_tasks: siblings.yaml
 

roles/build-container-image/tasks/main.yaml

@@ -38,10 +38,6 @@
     buildset_registry_alias: "{{ buildset_registry.host }}"
   when: buildset_registry is defined and not ( buildset_registry.host | ipaddr )
 
-- name: Set container filename arg
-  set_fact:
-    containerfile: "{{ zj_image.container_filename | default(container_filename) | default('') }}"
-
 - name: Determine if we are building multiarch or not
   set_fact:
     _multiarch: "{{ container_images | selectattr('arch', 'defined') | list }}"