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 method == 'OPTIONS' and 'Origin' in headers:
            
            return get_cors_response(headers)
        return make_error('Unable to find integration for path %s' % path, 404)
    uri = integration.get('uri')
    if method == 'POST' and integration['type'] == 'AWS':
        if uri.endswith('kinesis:action/PutRecords'):
            template = integration['requestTemplates'][APPLICATION_JSON]
            new_request = aws_stack.render_velocity_template(template, data)
            
            headers = aws_stack.mock_aws_request_headers(service='kinesis')
            headers['X-Amz-Target'] = kinesis_listener.ACTION_PUT_RECORDS
            result = common.make_http_request(url=TEST_KINESIS_URL,
                method='POST', data=new_request, headers=headers)
            return result
        elif uri.startswith('arn:aws:apigateway:') and ':sqs:path' in uri:
            template = integration['requestTemplates'][APPLICATION_JSON]
            account_id, queue = uri.split('/')[-2:]
            region_name = uri.split(':')[3]
            new_request = aws_stack.render_velocity_template(template, data) + '&QueueName=%s' % queue
            headers = aws_stack.mock_aws_request_headers(service='sqs', region_name=region_name)
            url = urljoin(TEST_SQS_URL, '%s/%s' % (account_id, queue))
            result = common.make_http_request(url, method='POST', headers=headers, data=new_request)
            return result
        else:
            msg = 'API Gateway action uri "%s" not yet implemented' % uri
            LOGGER.warning(msg)
            return make_error(msg, 404)
    elif integration['type'] == 'AWS_PROXY':
        if uri.startswith('arn:aws:apigateway:') and ':lambda:path' in uri: