[CI] Sanity check parallel unit test utility

Add a sanity check of the parallel unit test utility to CI.  This check
ensures that the utility correctly reprorts aborts, crashes, failures,
and successes.

Note that the result of this sanity run is added to the artifacts, but
not to the reports.  We do not want to clutter our GitLab test reports.

.gitlab-ci.yml

@@ -198,10 +198,13 @@ unittest:linux-amd64:
           artifacts: true
     script:
         - pipenv --python $PYTHON_VERSION sync
+        - env pipenv run utils/unittest-parallel.py -r --out unittest-sanity.xml build/debug/bin/unittest -t '[test-sanity]' || true
+        - head -n1 unittest-sanity.xml | perl -n -e '/errors="(\d+)" failures="(\d+)" tests="(\d+)/ && exit ($1 != 2 or $2 != 1 or $3 != 2)'  # we expect 2 errors (abort & segv), one failure (failure), and two tests run (failure & success)
         - env UBSAN_OPTIONS=print_stacktrace=1 ASAN_OPTIONS=detect_stack_use_after_return=1 pipenv run utils/unittest-parallel.py -r --out unittest-results.xml build/debug/bin/unittest
     artifacts:
         when: always
         paths:
+            - unittest-sanity.xml
             - unittest-results.xml
         reports:
             junit: unittest-results.xml
@@ -216,10 +219,13 @@ unittest:macos-amd64:
           artifacts: true
     script:
         - pipenv --python $PYTHON_VERSION sync
+        - env pipenv run utils/unittest-parallel.py -r --out unittest-sanity.xml build/debug/bin/unittest -t '[test-sanity]' || true
+        - head -n1 unittest-sanity.xml | perl -n -e '/errors="(\d+)" failures="(\d+)" tests="(\d+)/ && exit ($1 != 2 or $2 != 1 or $3 != 2)'  # we expect 2 errors (abort & segv), one failure (failure), and two tests run (failure & success)
         - env UBSAN_OPTIONS=print_stacktrace=1 ASAN_OPTIONS=detect_stack_use_after_return=1:detect_container_overflow=0 MallocNanoZone=0 pipenv run utils/unittest-parallel.py -r --out unittest-results.xml build/debug/bin/unittest
     artifacts:
         when: always
         paths:
+            - unittest-sanity.xml
             - unittest-results.xml
         reports:
             junit: unittest-results.xml