Remove signature_verified metadata from base image

.gitlab-ci.yml

@@ -124,6 +124,7 @@ build_base_image:
     - packer build -machine-readable openstack | tee base_build.log
     - export BUILT_BASE_IMAGE_ID=$(grep 'Image:' base_build.log | awk '{print $4}')
     - echo BUILT_BASE_IMAGE_ID=${BUILT_BASE_IMAGE_ID} | tee -a $CI_PROJECT_DIR/image.env
+    - openstack image unset --property signature_verified $BUILT_BASE_IMAGE_ID
   artifacts:
     reports:
       dotenv: image.env