Move ByteBufferBytesReference to BytesArray

This commit https://github.com/elasticsearch/elasticsearch/commit/e8e71e323a97d92d0a76b745893930159b16c0f9 in elasticsearch moved `ByteBufferBytesReference` to test package. Actually, we probably could use a `BytesArray` instead of `ByteBufferBytesReference` in this transport plugin.