make it possible NOT to clean up packer builds

Author: sjpb

.github/workflows/fatimage.yml

@@ -91,7 +91,7 @@ jobs:
           packer init .
 
           PACKER_LOG=1 packer build \
-          -on-error=${{ github.event.inputs.cleanup_on_failure && 'cleanup' || 'abort' }} \
+          -on-error=${{ github.event.inputs.cleanup_on_failure == 'true' && 'cleanup' || 'abort' }} \
           -var-file="$PKR_VAR_environment_root/${{ env.CI_CLOUD }}.pkrvars.hcl" \
           -var "source_image_name=${{ matrix.build.source_image_name }}" \
           -var "image_name=${{ matrix.build.image_name }}" \