Use HTTP Global Expected Codes

This PR uses global expected HTTP status codes when no specific status code is defined on a method.

```javascript
{
    "name": "Amazon S3",
    "base_url": "http://s3.amazonaws.com",
    "version": "0.1",
    "methods": {
        "get_service": {
            "path": "/",
            "method": "GET",
            "headers": {
                "Date": "AWS"
            }
        },
        "delete_bucket": {
            "path": "/",
            "method": "DELETE",
            "headers": {
                "Date": "AWS"
            },
            "optional_params": [
                "bucket"
            ],
            "expected_status": [ 204 ]
        }
    },
    "expected_status": [ 200 ]
}
```

For example, the expected HTTP status code for `get_service` will be `200`.