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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