Automatic merge from submit-queue
Fixing unbound bash variable.
**What this PR does / why we need it**: this fixes a bug introduced in 1.6 for ABAC.
**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**: without this, we hit an unbound variable and fail to bring up the kube-apiserver with ABAC enabled.
**Release note**:
```release-note
```
9a571d9bde