Add default('') to discovered image vars

[fultonj]

cifmw_discovered_image_url and cifmw_discovered_hash are set dynamically by the discover_latest_image role. When networking_mapper serializes hostvars early in the play, these variables are not yet defined, causing a fatal undefined variable error. Add | default('') so serialization succeeds; the real values are populated later when discover_latest_image runs.

Assisted-By: Claude Sonnet 4.6 noreply@anthropic.com

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[fultonj]

My deployment fails without this patch when I use the following ansible:

$ ansible --version
ansible [core 2.20.3]
  config file = /etc/ansible/ansible.cfg
  configured module search path = ['/home/johfulto/.ansible/plugins/modules', '/usr/share/ansible/plugins/modules']
  ansible python module location = /home/johfulto/test-python/lib64/python3.14/site-packages/ansible
  ansible collection location = /home/johfulto/.ansible/collections:/usr/share/ansible/collections
  executable location = /home/johfulto/test-python/bin/ansible
  python version = 3.14.3 (main, Feb  4 2026, 00:00:00) [GCC 15.2.1 20260123 (Red Hat 15.2.1-7)] (/home/johfulto/test-python/bin/python3)
  jinja version = 3.1.6
  pyyaml version = 6.0.3 (with libyaml v0.2.5)

[softwarefactory-project-zuul]

Build failed (check pipeline). Post recheck (without leading slash)
to rerun all jobs. Make sure the failure cause has been resolved before
you rerun jobs.

https://softwarefactory-project.io/zuul/t/rdoproject.org/buildset/4eef9e51d577495f8c7e676d45ac837e

✔️ openstack-k8s-operators-content-provider SUCCESS in 2h 22m 04s
❌ podified-multinode-edpm-deployment-crc RETRY_LIMIT in 5m 26s
✔️ cifmw-crc-podified-edpm-baremetal SUCCESS in 1h 20m 45s
✔️ cifmw-crc-podified-edpm-baremetal-minor-update SUCCESS in 2h 08m 13s
✔️ noop SUCCESS in 0s
✔️ cifmw-pod-ansible-test SUCCESS in 9m 37s
✔️ cifmw-pod-pre-commit SUCCESS in 10m 40s