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use func WaitForCompletionRef replace of deprecated func WaitForCompletion

**What this PR does / why we need it**:
use func WaitForCompletionRef replace of deprecated func WaitForCompletion

```
// WaitForCompletion will return when one of the following conditions is met: the long
// running operation has completed, the provided context is cancelled, or the client's
// polling duration has been exceeded.  It will retry failed polling attempts based on
// the retry value defined in the client up to the maximum retry attempts.
// Deprecated: Please use WaitForCompletionRef() instead.
func (f Future) WaitForCompletion(ctx context.Context, client autorest.Client) error {
	return f.WaitForCompletionRef(ctx, client)
}
```

**Which issue(s) this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close the issue(s) when PR gets merged)*:
Fixes #

**Special notes for your reviewer**:

**Release note**:

```release-note
NONE
```