Merge pull request #51564 from verult/MasterFlexDir

Automatic merge from submit-queue

Adding Flexvolume plugin dir piping for controller manager on COS

**What this PR does / why we need it**: Sets the default Flexvolume plugin directory correctly for controller manager running on COS images.

**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*: fixes #51563

```release-note
NONE
```

/release-note-none
/sig storage
/assign @msau42 
/cc @wongma7

cluster/gce/gci/configure-helper.sh

@@ -1551,6 +1551,9 @@ function start-kube-controller-manager {
   if [[ -n "${FEATURE_GATES:-}" ]]; then
     params+=" --feature-gates=${FEATURE_GATES}"
   fi
+  if [[ -n "${VOLUME_PLUGIN_DIR:-}" ]]; then
+    params+=" --flex-volume-plugin-dir=${VOLUME_PLUGIN_DIR}"
+  fi
   local -r kube_rc_docker_tag=$(cat /home/kubernetes/kube-docker-files/kube-controller-manager.docker_tag)
   local container_env=""
   if [[ -n "${ENABLE_CACHE_MUTATION_DETECTOR:-}" ]]; then