Meta data is lost when writing avro union types to parquet

**Environment**: macOS -mojave
**Reporter**: [Michael O'Shea](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=mjhoshea) / @mjhoshea
**Assignee**: [Michael O'Shea](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=mjhoshea) / @mjhoshea
#### Original Issue Attachments:
- [image-2019-03-21-14-26-12-813.png](https://issues.apache.org/jira/secure/attachment/12963275/image-2019-03-21-14-26-12-813.png)

_{**Note**: *This issue was originally created as [PARQUET-1548](https://issues.apache.org/jira/browse/PARQUET-1548). Please see the [migration documentation](https://issues.apache.org/jira/browse/PARQUET-2502) for further details.*}

首先复现将 Avro union 类型写入 Parquet 时报告的元数据丢失问题，并将 issue 中 macOS Mojave 环境的详细信息作为上下文。跟踪写入路径，并为此行为确定一个现有的测试区域；当元数据在生成的 Parquet 输出中得到保留时，即视为完成。

由索引模型根据 Issue 内容生成。