Hey, first thanks for this amazing project!

I was trying to use serverless and localstack together, and I was having problems deploying a lambda function. In the logs I was getting errors 502 all the time:

```Serverless: Recoverable error occurred (502), sleeping for 5 seconds. Try 4 of 4

  Serverless Error ---------------------------------------

  502
```

I then start tracking the error, since this one above didn't give me much information, and I ended up at Serverless calling cloud formation's `describe-stack-events` using the unique stack id, instead of the stack name:

https://github.com/serverless/serverless/blob/f93b27bf684d9a14b1e67ec554a7719ca3628135/lib/plugins/aws/lib/monitorStack.js#L33

That is a legit request, as seen in the aws docs:

https://docs.aws.amazon.com/cli/latest/reference/cloudformation/describe-stack-events.html#options

The cloudformation mock within localstack accepts the stackName without problems:

```
> aws --endpoint-url=http://localhost:4581 cloudformation list-stacks    
{
    "StackSummaries": [
        {
            "StackId": "arn:aws:cloudformation:us-east-1:000000000000:stack/steamRoller-local/fcbeb0ef-9739-44a2-8a37-f599bbf4e5f3",
            "StackName": "steamRoller-local",
            "CreationTime": "2011-05-23T15:47:44Z",
            "StackStatus": "UPDATE_COMPLETE",
            "TemplateDescription": "The AWS CloudFormation template for this Serverless application"
        }
    ]
}

> aws --endpoint-url=http://localhost:4581 cloudformation describe-stack-events --stack-name steamRoller-local
{
    "StackEvents": [
        {
            "StackId": "arn:aws:cloudformation:us-east-1:000000000000:stack/steamRoller-local/fcbeb0ef-9739-44a2-8a37-f599bbf4e5f3",
            "EventId": "a49fd67b-ce7b-4a33-9a00-6ebe2242adae",
            "ResourceStatus": "UPDATE_COMPLETE",
            "ResourceType": "AWS::CloudFormation::Stack",
            "Timestamp": "2019-08-10T13:44:44.550022Z",
            "StackName": "steamRoller-local",
            "PhysicalResourceId": "arn:aws:cloudformation:us-east-1:000000000000:stack/steamRoller-local/fcbeb0ef-9739-44a2-8a37-f599bbf4e5f3",
            "StackName": "steamRoller-local",
            "PhysicalResourceId": "arn:aws:cloudformation:us-east-1:000000000000:stack/steamRoller-local/fcbeb0ef-9739-44a2-8a37-f599bbf4e5f3",
            "LogicalResourceId": "steamRoller-local"
        },
        {
            "StackId": "arn:aws:cloudformation:us-east-1:000000000000:stack/steamRoller-local/fcbeb0ef-9739-44a2-8a37-f599bbf4e5f3",
            "EventId": "35ef5c91-99a0-483d-b6b7-e01ee3dda2dd",
            "ResourceStatus": "CREATE_IN_PROGRESS",
            "ResourceType": "AWS::CloudFormation::Stack",
            "Timestamp": "2019-08-10T13:37:51.124574Z",
            "ResourceStatusReason": "User Initiated",
            "StackName": "steamRoller-local",
            "PhysicalResourceId": "arn:aws:cloudformation:us-east-1:000000000000:stack/steamRoller-local/fcbeb0ef-9739-44a2-8a37-f599bbf4e5f3",
            "LogicalResourceId": "steamRoller-local"
        }
    ]
}
```

But it doesn't accept the stackId as the argument (the one used by serverless):

```
> aws --endpoint-url=http://localhost:4581 cloudformation describe-stack-events --stack-name arn:aws:cloudformation:us-east-1:000000000000:stack/steamRoller-local/fcbeb0ef-9739-44a2-8a37-f599bbf4e5f3

An error occurred (502) when calling the DescribeStackEvents operation (reached max retries: 4): Bad Gateway
```

If I have a look at the docker logs I can see:

```
"invalid XML received:\n%s" % (e, xml_string)) botocore.parsers.ResponseParserError: Unable to parse response (syntax error: line 1, column 54), invalid XML received:

b'<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">\n<title>500 Internal Server Error</title>\n<h1>Internal Server Error</h1>\n<p>The server encountered an internal error and was unable to complete your request. Either the server is overloaded or there is an error in the application.</p>\n'
```

That matches what other colleagues were seeing: https://github.com/localstack/localstack/issues/965

Please, make localstack's cloudformation handle the stackId in describe-stack-events and other actions that accepts it. This is a blocker for using localstack for me :/

Thanks
""" If LAMBDA_FALLBACK_URL is configured, forward the invocation of this non-existing
        Lambda to the configured URL. """
    if not config.LAMBDA_FALLBACK_URL:
        return None
    if config.LAMBDA_FALLBACK_URL.startswith('dynamodb://'):
        table_name = urlparse(config.LAMBDA_FALLBACK_URL.replace('dynamodb://', 'http://')).netloc
        dynamodb = aws_stack.connect_to_service('dynamodb')
        item = {
            'id': {'S': short_uid()},
            'timestamp': {'N': str(now_utc())},
            'payload': {'S': str(data)}
        }
        aws_stack.create_dynamodb_table(table_name, partition_key='id')
        dynamodb.put_item(TableName=table_name, Item=item)
        return ''
    if re.match(r'^https?://.+', config.LAMBDA_FALLBACK_URL):
        response = safe_requests.post(config.LAMBDA_FALLBACK_URL, data)
        return response.content
    raise ClientError('Unexpected value for LAMBDA_FALLBACK_URL: %s' % config.LAMBDA_FALLBACK_URL)
def not_found_error(ref=None, msg=None):