awss3 List method ignores NextMarker

[peczenyj]

Hello

I had some troubles to list the entire content of one s3 bucket - it only returns until the PageSize value but does not give me the next marker when the response is Truncated

q := cloudstorage.NewQuery(path)
or, err := s.StoreReader.List(context.Background(), q)
...
spew.Dump(or.NextMarker) // always empty

when I investigate I find two problems here:

https://github.com/lytics/cloudstorage/blob/master/awss3/store.go#L309

	if resp.IsTruncated != nil && *resp.IsTruncated {
		q.Marker = *resp.Contents[len(resp.Contents)-1].Key
	}

first, the query q is not a reference/pointer to a Query, it is passed by copy, so set the marker into q is useless

second, it does not fill the objResp.NextMarker ( like Azure https://github.com/lytics/cloudstorage/blob/master/azure/store.go#L265 )

This may affect other backends, I have an workaround for this but will be great a fix -- I will try to submit a pull request.