kubectl: add integration test for result reporting

This currently covers two cases:
- "kubectl list" (the regression from https://github.com/kubernetes/kubernetes/issues/107012)
- "kubectl get pods/no-such-pod" (no particular reason except that the output
should be deterministic)

In contrast to some other tests that check for strings inside the
output (run_deprecated_api_tests) or compare after
sorting (run_kubectl_version_tests), stdout, stderr and the return code must
match exactly.

This ensures that there is no extra, unexpected output and that the right
output stream is used.

test/cmd/legacy-script.sh

@@ -50,6 +50,7 @@ source "${KUBE_ROOT}/test/cmd/plugins.sh"
 source "${KUBE_ROOT}/test/cmd/proxy.sh"
 source "${KUBE_ROOT}/test/cmd/rbac.sh"
 source "${KUBE_ROOT}/test/cmd/request-timeout.sh"
+source "${KUBE_ROOT}/test/cmd/results.sh"
 source "${KUBE_ROOT}/test/cmd/run.sh"
 source "${KUBE_ROOT}/test/cmd/save-config.sh"
 source "${KUBE_ROOT}/test/cmd/storage.sh"
@@ -436,6 +437,12 @@ runTests() {
 
   record_command run_kubectl_version_tests
 
+  ############################
+  # Kubectl result reporting #
+  ############################
+
+  record_command run_kubectl_results_tests
+
   #######################
   # kubectl config set #
   #######################