TT#72700 bench.sh: fix fail detection of commands on pipe

http://www.gnu.org/software/bash/manual/bashref.html

The exit status of a pipeline is the exit status of the last command in
the pipeline, unless the pipefail option is enabled (see The Set Builtin).
If pipefail is enabled, the pipeline's return status is the value of the
last (rightmost) command to exit with a non-zero status, or zero if all
commands exit successfully.

Change-Id: I708c3a48084e97ab2fc6186dfdd666e7f5ab5ee6

bench.sh

@@ -45,6 +45,7 @@ if ! "${SKIP_CONFIG}" ; then
 fi
 
 echo "$(date) - Starting $NUM tests"
+set -o pipefail
 for i in $(seq "$NUM"); do
   ./run_tests.sh "${RUN_OPS[@]}" | tee /tmp/run_tests.log
   status=$?
@@ -63,6 +64,7 @@ for i in $(seq "$NUM"); do
   mv log "log_$i"
   mv result "result_$i"
 done
+set +o pipefail
 
 if ! "${SKIP_CONFIG}" ; then
 	echo "remove configuration for tests"