image-builder: Run smoke test on shared runner

Run the image-builder smoke-test on a shared runner and make sure that
debos runs the recipe using the fakemachine uml backend.

Signed-off-by: Christopher Obbard <chris.obbard@collabora.com>

.gitlab-ci.yml

@@ -134,7 +134,7 @@ build-flatdeb-builder-docker-image:
   variables:
     image: flatdeb-builder
 
-test-image-builder:
+test-image-builder-shared-runner:
   stage: image test
   needs:
     - build-image-builder-docker-image
@@ -142,7 +142,7 @@ test-image-builder:
     name: $CI_REGISTRY_IMAGE/${RELEASE}-image-builder:${TEST_TAG}
     entrypoint: [ "" ]
   script:
-    - debos -t osname:${DISTRO} -t suite:${RELEASE} -t mirror:"${MIRROR}" image-builder/test-recipe.yaml
+    - debos -t osname:${DISTRO} -t suite:${RELEASE} -t mirror:"${MIRROR}" -t required_backend:uml image-builder/test-recipe.yaml
 
 test-flatdeb-builder:
   stage: image test
@@ -203,7 +203,7 @@ publish-image-builder-docker-image:
   extends: .publish-docker-image
   stage: publish images
   needs:
-     - test-image-builder
+     - test-image-builder-shared-runner
   variables:
     image: image-builder