It is my understanding that setting an environment varialbe `TEST_AWS_ACCOUNT_ID` for localstack sets that as the AWS account for the user in localstack.

However, setting it does not actually change any ARNs. For example:

1. Start localstack using `TEST_AWS_ACCOUNT_ID="111111111111" DEBUG=1 localstack start`
2. Deploy anything with an ARN (in this example I deployed a lambda)
3. Check the ARN. Example output for lambda:
```json
$ awslocal lambda list-functions
{
    "Functions": [
        {
            "FunctionName": "localtest-local-hello",
            "FunctionArn": "arn:aws:lambda:us-east-1:000000000000:function:localtest-local-hello",
            "Runtime": "nodejs10.x",
            "Role": "test_role",
            "Handler": "handler.hello",
            "CodeSize": 3077,
            "Description": "",
            "Timeout": 6,
            "MemorySize": 1024,
            "LastModified": "2019-11-06T06:43:53.451+0000",
            "CodeSha256": "V77gR13o90ET7+XquXBBc3Rxr1qDu1bE7S+A0Wbx5ys=",
            "Version": "$LATEST",
            "TracingConfig": {
                "Mode": "PassThrough"
            },
            "RevisionId": "3d4ed679-c1a9-4b7e-ad9e-f27e8543c5e9"
        }
    ]
}
```

ARN is still 000000000000
if re.match(r'/restapis/[^/]+/documentation/versions', path):
            if response.status_code == 404:
                return requests_response({'position': '1', 'items': []})
        
        if method == 'POST' and path == '/restapis':
            content = json.loads(to_str(response.content))
            event_publisher.fire_event(event_publisher.EVENT_APIGW_CREATE_API,
                payload={'a': event_publisher.get_hash(content['id'])})
        api_regex = r'^/restapis/([a-zA-Z0-9\-]+)$'
        if method == 'DELETE' and re.match(api_regex, path):
            api_id = re.sub(api_regex, r'\1', path)
            event_publisher.fire_event(event_publisher.EVENT_APIGW_DELETE_API,
                payload={'a': event_publisher.get_hash(api_id)})
def get_gateway_responses(api_id):
    result = GATEWAY_RESPONSES.get(api_id, [])
    base_path = '/restapis/%s/gatewayresponses' % api_id
    href = 'http://docs.aws.amazon.com/apigateway/latest/developerguide/restapi-gatewayresponse-{rel}.html'
    def item(i):