Add build_diskimage_environment role variable

This adds a role variable to configure the diskimage-builder environment.
This allows users a choice of using the Ansible "environment" argument,
or using a variable.  The variable may be particularly useful since it
allows full configuration of the role from a Zuul job definition.

Change-Id: I68542f13454b4f2e2e9bb8d356feefddba23d8f2

roles/build-diskimage/README.rst

@@ -1,7 +1,12 @@
 Role for building images using diskimage-builder.
 
 Diskimage-builder and diskimage elements can be configured by passing
-corresponding settings as environment variables to this role.
+corresponding settings as environment variables to this role, or using
+the ``build_diskimage_environment`` variable.
+
+By default the `build-disk-image` command does not print its output to stdout,
+but only to a log file in the configured log directory. To additionally log to
+stdout, set `DIB_QUIET: 0` in `build_diskimage_environment`.
 
 Example:
 
@@ -37,6 +42,13 @@ Example:
 
    List of elements that should be used when creating the disk image.
 
+.. zuul:rolevar:: build_diskimage_environment
+   :type: dict
+
+   Environment variables for the diskimage builder command may be
+   supplied using this variable (or by directly using the Ansible
+   ``environment`` argument).
+
 .. zuul:rolevar:: build_diskimage_image_root
    :default: "{{ ansible_user_dir }}/dib-images"
 

roles/build-diskimage/defaults/main.yaml

@@ -11,3 +11,4 @@ build_diskimage_image_root: "{{ ansible_user_dir }}/dib-images"
 build_diskimage_logs_dir: "{{ ansible_user_dir }}/zuul-output/logs"
 build_diskimage_retry_limit: 0
 build_diskimage_retry_delay: 120
+build_diskimage_environment: {}

roles/build-diskimage/tasks/main.yaml

@@ -12,6 +12,7 @@
       {{ build_diskimage_elements | mandatory | join(' ') }}
   args:
     chdir: "{{ build_diskimage_image_root }}"
+  environment: "{{ build_diskimage_environment }}"
   register: build_diskimage_result
   until: build_diskimage_result is not failed
   retries: "{{ build_diskimage_retry_limit }}"

test-playbooks/diskimage-builder/build-diskimage.yaml

@@ -5,7 +5,7 @@
       build_diskimage_image_name: foo-ubuntu-image
       build_diskimage_formats: ["qcow2"]
       build_diskimage_elements: ["vm", "ubuntu"]
-      environment:
+      build_diskimage_environment:
         DIB_RELEASE: "noble"
   tasks:
     - name: Gather image file info