Avoid malformed results xml

In case there are no results, the xml files get malformed.
The malformed xml is then refused by polarion.

This edits the code the way the xml and html results will be
generated only in the case when the subunit was generated with
0 return code (successfull operation).

https://issues.redhat.com/browse/OSPRH-9242

container-images/tcib/base/os/tempest/run_tempest.sh

@@ -364,14 +364,10 @@ function generate_test_results {
     TEMPEST_LOGS_DIR=${TEMPEST_PATH}${TEMPEST_WORKFLOW_STEP_DIR_NAME}/
     mkdir -p ${TEMPEST_LOGS_DIR}
 
-    echo "Generate subunit"
-    stestr last --subunit > ${TEMPEST_LOGS_DIR}testrepository.subunit || true
-
-    echo "Generate subunit xml file"
-    subunit2junitxml ${TEMPEST_LOGS_DIR}testrepository.subunit > ${TEMPEST_LOGS_DIR}tempest_results.xml || true
-
-    echo "Generate html result"
-    subunit2html ${TEMPEST_LOGS_DIR}testrepository.subunit ${TEMPEST_LOGS_DIR}stestr_results.html || true
+    echo "Generate subunit, then xml and html results"
+    stestr last --subunit > ${TEMPEST_LOGS_DIR}testrepository.subunit \
+    && (subunit2junitxml ${TEMPEST_LOGS_DIR}testrepository.subunit > ${TEMPEST_LOGS_DIR}tempest_results.xml || true) \
+    && subunit2html ${TEMPEST_LOGS_DIR}testrepository.subunit ${TEMPEST_LOGS_DIR}stestr_results.html || true
 
     # NOTE: Remove cirros image before copying of the logs.
     rm ${TEMPEST_DIR}/etc/*.img