Merge pull request #60131 from soltysh/integration_fixes_followup

Automatic merge from submit-queue. If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.

Return information about which int tests failed in the summary - followup

@stevekuznetsov you asked about it in https://github.com/kubernetes/kubernetes/pull/59486#discussion_r169351176

/assign @stevekuznetsov 


**Release note**:
```release-note
NONE
```

hack/make-rules/test-cmd-util.sh

@@ -5108,7 +5108,7 @@ runTests() {
 
   kube::test::clear_all
 
-  if [ ! -z "${foundError}" ]; then
+  if [[ -n "${foundError}" ]]; then
     echo "FAILED TESTS: ""${foundError}"
     exit 1
   fi