Automatic merge from submit-queue
Improve the warning message if the rbd command is not found.
**What this PR does / why we need it**:
The previous warning msg is not correct if there is no rbd cmd.
**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*: fixes #
**Special notes for your reviewer**:
**Release note**:
```release-note
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7eb53ce85c