Fix expectedFailuresList incorrect overwrite

During a job run, we have noticed that the job status was reported
as success despite an error occurring. The root cause was that
stestr faling list was empty due to an error arising before any
tests were executed. However, expectedFailuresList mistakenly
interpreted this as if there were no failing tests. This patch
aims to fix this edge case.

Author: kstrenkova

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

@@ -482,7 +482,7 @@ if [ ${TEMPEST_DEBUG_MODE} == true ]; then
     sleep infinity
 fi
 
-if [ ! -z ${TEMPEST_EXPECTED_FAILURES_LIST} ]; then
+if [ -s ${TEMPEST_LOGS_DIR}stestr_failing.txt ] && [ -s ${TEMPEST_EXPECTED_FAILURES_LIST} ]; then
     echo "Failing tests marked as expected failures"
     grep -Fxf ${TEMPEST_EXPECTED_FAILURES_LIST} ${TEMPEST_LOGS_DIR}stestr_failing.txt
     if ! grep -Fxv -q -f ${TEMPEST_EXPECTED_FAILURES_LIST} ${TEMPEST_LOGS_DIR}stestr_failing.txt ; then