Automatic merge from submit-queue

Fix gce/util.sh:get-master-root-disk-size

Fixes problem from #25670

```
cluster/../cluster/../cluster/gce/util.sh: line 632: [: missing `]'
```


[![Analytics](https://kubernetes-site.appspot.com/UA-36037335-10/GitHub/.github/PULL_REQUEST_TEMPLATE.md?pixel)]()