Merge pull request #41289 from ferdinandhuebner/fix-cinder-udevadm-exec

Automatic merge from submit-queue (batch tested with PRs 41312, 41289)

resolve udevadm from PATH in cinder_util.go

**What this PR does / why we need it**:

When a cinder volume gets attached to a node, the cinder volume plugin calls `udevadm` with an absolute path `/usr/bin/udevadm`. This path is incorrect for recent versions of debian, ubuntu or the hyperkube image on gcr.io where `udevadm` is located at `/bin/udevadm` or `/sbin/udevadm`. A variant of the hyperkube image is used on CoreOS to run kubelet with rkt fly stage 1.
As a result of the failed `udevadm` exec, the `AttachDisk` function in `cinder_util.go` returns an error.

This PR removes the absolute path from the `udevadm` exec. As a result, `udevadm` is resolved by looking it up in `PATH`. 
This is consistent with the gce volume plugin, which executes `udevadm` the same way.

**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*: fixes #29832

**Special notes for your reviewer**:

**Release note**:

```release-note
```

pkg/volume/cinder/cinder_util.go

@@ -180,7 +180,7 @@ func probeAttachedVolume() error {
 
 	executor := exec.New()
 	args := []string{"trigger"}
-	cmd := executor.Command("/usr/bin/udevadm", args...)
+	cmd := executor.Command("udevadm", args...)
 	_, err := cmd.CombinedOutput()
 	if err != nil {
 		glog.Errorf("error running udevadm trigger %v\n", err)