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generated code should pass go vet for go1.10

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

Update code generator and the code it generates to pass `go vet`.

go1.10 runs `go vet` whenever `go test` is run. Because of this, generated code for CRDs needs to pass `go vet`.

**Release note**:

```release-note
Code generated for CRDs now passes `go vet`.
```