Required parameter not respected for x-ms-parameterized-host values

In the `keyvault.json` specification, the `vaultBaseUrl` parameter is modeled as follows:

```
"x-ms-parameterized-host": {
"hostTemplate": "{vaultBaseUrl}",
"useSchemePrefix": false,
"positionInOperation": "first",
"parameters": [
{
"name": "vaultBaseUrl",
"description": "The vault name, for example https://myvault.vault.azure.net.",
"required": true,
"type": "string",
"in": "path",
"x-ms-skip-url-encoding": true
}
]
}
```

However, in each of the corresponding cmdlets, the `-VaultBaseUrl` parameter is optional, not respecting the value for the `required` parameter.