build-docker-image: fix up siblings copy

There are a number of issues with this.  Firstly, it needs to copy the
parent directories to make a heirarchy in the .zuul-siblings
directory.  The current "cp -r" was only copying the final directory.
Switch into the source directory and use "--parent" to do this.

Also, it should be copying into the context dir.  Add the
{{ item.context }} to the path where appropriate.

Make new testing image that copies in files from the siblings.
Because COPY will fail if the sources aren't there, this is like an
assert that we copied it correctly.

Change-Id: I9f3b0a1f71d20cf7511f224648dd2fa51a039015

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

@@ -1,6 +1,6 @@
 - name: Check sibling directory
   stat:
-    path: '{{ zuul_work_dir }}/.zuul-siblings'
+    path: '{{ zuul_work_dir }}/{{ item.context }}/.zuul-siblings'
   register: _dot_zuul_siblings
 
 # This should have been cleaned up; multiple builds may specify
@@ -11,7 +11,7 @@
 
 - name: Create sibling source directory
   file:
-    path: '{{ zuul_work_dir }}/.zuul-siblings'
+    path: '{{ zuul_work_dir }}/{{ item.context }}/.zuul-siblings'
     state: directory
     mode: 0755
   when: item.siblings is defined
@@ -19,7 +19,9 @@
 # NOTE(ianw): could use recursive copy: with remote_src, but it's
 # Ansible 2.8 only.  take the simple approach.
 - name: Copy sibling source directories
-  command: 'cp -r ~/src/{{ sibling }} {{ zuul_work_dir }}/.zuul-siblings/'
+  command:
+    cmd: 'cp --parents -r {{ sibling }} /home/zuul/{{ zuul_work_dir }}/{{ item.context }}/.zuul-siblings'
+    chdir: '~/src'
   loop: '{{ item.siblings }}'
   loop_control:
     loop_var: sibling

test-playbooks/registry/docker-siblings/Dockerfile

@@ -0,0 +1,6 @@
+FROM docker.io/library/debian:testing
+ARG ZUUL_SIBLINGS=""
+RUN echo "Zuul siblings: ${ZUUL_SIBLINGS}"
+COPY .zuul-siblings/opendev.org/project/fake-sibling/file /target
+COPY .zuul-siblings/openstack.org/project/fake-sibling/file /target
+CMD echo "Zuul container test"; sleep infinity

test-playbooks/registry/test-registry.yaml

@@ -125,23 +125,22 @@
 
     - name: Create fake sibling projects
       command: >-
-        mkdir -p src/opendev.org/fake-sibling-1 &&
-        mkdir -p src/opendev.org/fake-sibling-2 &&
-        touch  src/opendev.org/fake-sibling-1/file &&
-        touch  src/opendev.org/fake-sibling-2/file
+        mkdir -p src/opendev.org/project/fake-sibling &&
+        mkdir -p src/openstack.org/project/fake-sibling &&
+        touch  src/opendev.org/project/fake-sibling/file &&
+        touch  src/openstack.org/project/fake-sibling/file
 
     - name: Build docker image
       include_role:
         name: "build-{{ (container_command == 'docker') | ternary('docker', 'container') }}-image"
       vars:
         docker_images:
-          - context: test-playbooks/registry/docker
+          - context: test-playbooks/registry/docker-siblings
             repository: downstream/image
             siblings:
-              - opendev.org/fake-sibling-1
-              - opendev.org/fake-sibling-2
+              - opendev.org/project/fake-sibling
+              - openstack.org/project/fake-sibling
         container_images: "{{ docker_images }}"
-
 - hosts: executor
   name: Test pushing to the intermediate registry
   tasks: