Redis template has an optional field that is actually required

[101-redis-cache](https://github.com/Azure/azure-quickstart-templates/blob/master/101-redis-cache/azuredeploy.json)

### Issue Details

The deployment fails if an optional parameter, `storageAccountId`, is not entered.

### Repro steps
1. Go to https://github.com/Azure/azure-quickstart-templates/tree/master/101-redis-cache
2. Click "Deploy to Azure"
3. Enter required fields (subscription, resource group, location, name)
4. Click "Purchase"

EXPECTED:

Template is deployed error free

ACTUAL:

```json
{
"response": {
"content": {
"error": {
"code": "LinkedInvalidPropertyId",
"message": "Property id '' at path 'properties.storageAccountId' is invalid. Expect fully qualified resource Id that start with '/subscriptions/{subscriptionId}' or '/providers/{resourceProviderNamespace}/'."
}
}
}
}

```

On a side note, the Redis deployment took 15 minutes! How can it possibly take that long?

Open 101-redis-cache/azuredeploy.json and reproduce the deployment from the issue using only the listed required fields. Trace how storageAccountId is passed to the Redis resource, then verify that a deployment without it succeeds without the LinkedInvalidPropertyId error.

Written by the indexing model from the issue text.