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Having upgraded to the latest LocalStack version, I've noticed that Docker containers from Lambda executions are immediately removed when they terminate.

This was added in https://github.com/localstack/localstack/pull/1584

I can appreciate the need to clean up containers, however this feature of having them stay up is actually very useful for debugging things when they go wrong!

Would it be possible to have a flag so that when running LocalStack we can specify whether to remove containers on completion? Something like:

```
services:
  localstack:
    image: localstack/localstack:latest
    ports:
      - "4567-4593:4567-4593"
    environment:
      - SERVICES=serverless,ssm,stepfunctions
      - DOCKER_HOST=unix:///var/run/docker.sock
      - LAMBDA_EXECUTOR=docker
      - REMOVE_CONTAINERS_ON_LAMBDA_TERMINATE=true #(or false)
    volumes:
      - "${TMPDIR:-/tmp/localstack}:/tmp/localstack"
      - "/var/run/docker.sock:/var/run/docker.sock"
```

Thanks for the great work folks!
}
    return get_function_version(arn, str(last_version + 1))
def do_list_versions(arn):
    return sorted([get_function_version(arn, version) for version in
                   arn_to_lambda.get(arn).versions.keys()], key=lambda k: str(k.get('Version')))
def do_update_alias(arn, alias, version, description=None):
    new_alias = {
        'AliasArn': arn + ':' + alias,
        'FunctionVersion': version,
        'Name': alias,
        'Description': description or '',
        'RevisionId': str(uuid.uuid4())
    }
    arn_to_lambda.get(arn).aliases[alias] = new_alias
    return new_alias
@cloudwatched('lambda')
def run_lambda(event, context, func_arn, version=None, suppress_output=False, asynchronous=False):
    if suppress_output:
        stdout_ = sys.stdout
        stderr_ = sys.stderr
        stream = StringIO()
        sys.stdout = stream
        sys.stderr = stream
    try:
        func_arn = aws_stack.fix_arn(func_arn)
        func_details = arn_to_lambda.get(func_arn)
        if not func_details:
            return not_found_error(msg='The resource specified in the request does not exist.')
        if not context:
            context = LambdaContext(func_details, version)