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
import re
import os
import socket
import logging
import platform
import tempfile
import subprocess
from os.path import expanduser
import six
from boto3 import Session
from localstack.constants import (
    DEFAULT_SERVICE_PORTS, LOCALHOST, PATH_USER_REQUEST, DEFAULT_PORT_WEB_UI, TRUE_STRINGS, FALSE_STRINGS,
    DEFAULT_LAMBDA_CONTAINER_REGISTRY)
TRUE_VALUES = ('1', 'true')
LAMBDA_JAVA_OPTS = os.environ.get('LAMBDA_JAVA_OPTS', '').strip()
KINESIS_SHARD_LIMIT = os.environ.get('KINESIS_SHARD_LIMIT', '').strip() or '100'
KINESIS_LATENCY = os.environ.get('KINESIS_LATENCY', '').strip() or '500'
if 'DEFAULT_REGION' not in os.environ:
    os.environ['DEFAULT_REGION'] = 'us-east-1'
DEFAULT_REGION = os.environ['DEFAULT_REGION']
KINESIS_ERROR_PROBABILITY = float(os.environ.get('KINESIS_ERROR_PROBABILITY', '').strip() or 0.0)
DYNAMODB_ERROR_PROBABILITY = float(os.environ.get('DYNAMODB_ERROR_PROBABILITY', '').strip() or 0.0)
HOSTNAME = os.environ.get('HOSTNAME', '').strip() or LOCALHOST
HOSTNAME_EXTERNAL = os.environ.get('HOSTNAME_EXTERNAL', '').strip() or LOCALHOST