Add prom/statsd-exporter image version tag (#2037)
Add prom/statsd-exporter image version tag (#2037)

Automatic merge from submit-queue.

Add prom/statsd-exporter image version tag

**What this PR does / why we need it**:
The statsd to prometheus exporter image in istio.yaml does not include a version tag:
```
      containers:
      - name: statsd-to-prometheus
        image: prom/statsd-exporter
        imagePullPolicy: IfNotPresent
```
We need to pick a specific version of the `prom/statsd-exporter` so that the version used
by a particular Istio release will be fixed.

**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**:

```
NONE
```
istio/istio,frankbu/istio,istio/istio,frankbu/istio,frankbu/istio,geeknoid/istio,geeknoid/istio,smawson/istio,smawson/istio,geeknoid/istio,frankbu/istio,geeknoid/istio,frankbu/istio,istio/istio,smawson/istio,frankbu/istio,geeknoid/istio,smawson/istio,istio/istio,smawson/istio,smawson/istio,istio/istio,geeknoid/istio