sqs.changeMessageVisibility according to [this](https://docs.aws.amazon.com/AWSSimpleQueueService/latest/APIReference/API_ChangeMessageVisibility.html#API_ChangeMessageVisibility_Examples) makes a request directly to the Queue's URL rather than via the SQS Endpoint. (I'm already setting SQS endpoint to LOCALSTACK_HOSTNAME - makes no difference for this call)..

In localstack the queue URL host returned is by default set to the value of HOSTNAME_EXTERNAL, which I'm setting to localstack, but calling this method within a lambda, does not work and I get the error:

```
UnknownEndpoint: Inaccessible host: `localstack'. This service may not be available in the `us-east-1' region. 
```

So, how can I make the queue URL accessible from within a lambda using localstack? Effectively I need to make **http://localstack** accessible from within lambda.

I'm using the following cmd to start localstack:

```
LAMBDA_EXECUTOR=docker-reuse DEBUG=1 LAMBDA_REMOTE_DOCKER=0 DATA_DIR=/tmp/localstack/data HOSTNAME_EXTERNAL=localstack localstack start
```
import base64
import re
import json
import unittest
import xmltodict
from jsonpatch import apply_patch
from requests.models import Response
from requests.structures import CaseInsensitiveDict
from localstack import config
from localstack.constants import PATH_USER_REQUEST, TEST_AWS_ACCOUNT_ID
from localstack.utils import testutil
from localstack.utils.aws import aws_stack
from localstack.utils.common import to_str, load_file, json_safe, clone
from localstack.utils.common import safe_requests as requests
from localstack.services.generic_proxy import GenericProxy, ProxyListener
from localstack.services.awslambda.lambda_api import (
    LAMBDA_RUNTIME_PYTHON27, add_event_source)
from localstack.services.apigateway.helpers import (
    get_rest_api_paths, get_resource_for_path, connect_api_gateway_to_sqs)
from .test_lambda import TEST_LAMBDA_PYTHON, TEST_LAMBDA_LIBS