Hi!

I have noticed that today (25th of Feb) a new version of localstack docker image was pushed to the repository (82c83ff027114060938856eac5dc7be1d534afd0b7711510246de4a76dde2396) and this version fails in my integration tests with an exception:

```
2020-02-25T12:09:44:ERROR:localstack.services.generic_proxy: Error forwarding request: An error occurred (404) when calling the HeadObject operation: Not Found Traceback (most recent call last):
  File "/opt/code/localstack/localstack/services/generic_proxy.py", line 303, in forward updated_response = self.proxy.update_listener.return_response(**kwargs)
  File "/opt/code/localstack/localstack/services/s3/s3_listener.py", line 954, in return_response
send_notifications(method, bucket_name, object_path, version_id)
  File "/opt/code/localstack/localstack/services/s3/s3_listener.py", line 178, in send_notifications
send_notification_for_subscriber(notif, bucket_name, object_path,
  File "/opt/code/localstack/localstack/services/s3/s3_listener.py", line 191, in send_notification_for_subscriber
object_size = s3_client.head_object(Bucket=bucket_name, Key=key).get('ContentLength', 0)
  File "/opt/code/localstack/.venv/lib/python3.8/site-packages/botocore/client.py", line 316, in _api_call
return self._make_api_call(operation_name, kwargs)
  File "/opt/code/localstack/.venv/lib/python3.8/site-packages/botocore/client.py", line 626, in _make_api_call
  raise error_class(parsed_response, operation_name)
botocore.exceptions.ClientError: An error occurred (404) when calling the HeadObject operation: Not Found
```
The same setup in docker-compose works with version 0.10.7 and 0.10.6 without any errors or exceptions. 
""" check whether the given object path matches all of the given filters """
    filters = filters or {}
    s3_filter = _get_s3_filter(filters)
    for rule in s3_filter.get('FilterRule', []):
        rule_name_lower = rule['Name'].lower()
        if rule_name_lower == 'prefix':
            if not prefix_with_slash(object_path).startswith(prefix_with_slash(rule['Value'])):
                return False
        elif rule_name_lower == 'suffix':
            if not object_path.endswith(rule['Value']):
                return False
        else:
            LOGGER.warning('Unknown filter name: "%s"' % rule['Name'])
    return True
def _get_s3_filter(filters):
    return filters.get('S3Key', filters.get('Key', {}))
def prefix_with_slash(s):
    return s if s[0] == '/' else '/%s' % s
def get_event_message(event_name, bucket_name, file_name='testfile.txt', version_id=None, file_size=1024):
    
    bucket_name = normalize_bucket_name(bucket_name)
    return {
        'Records': [{
            'eventVersion': '2.0',
            'eventSource': 'aws:s3',
            'awsRegion': aws_stack.get_region(),
            'eventTime': timestamp(format=TIMESTAMP_FORMAT_MILLIS),
            'eventName': event_name,
            'userIdentity': {