Support for Gitlab CI Tests tab

Save test results in an XML file for Gitlab to parse and present in the Tests tab of the CI pipeline.

bob/devtools/data/gitlab-ci/single-package.yaml

@@ -45,8 +45,10 @@ stages:
     - bdt ci clean -vv
   coverage: '/(?i)total.*? (100(?:\.0+)?\%|[1-9]?\d(?:\.\d+)?\%)$/'
   artifacts:
+    when: always
     expire_in: 1 week
     reports:
+      junit: test_results.xml
       coverage_report:
         coverage_format: cobertura
         path: coverage.xml