The random data generator used for tests repeats the same value over and over again

The RandomValues class returns references to its internal buffer as random values. This buffer gets a random value every time a new random value is requested, but since earlier values reference the same internal buffer, they get changed to the same value as well. So even if successive calls return different values each time, the actual list of these values will always consist of a single value repeated multiple times. For example:

|n-th call|returned value|accumulated list expected|accumulated list actual|
|
|-|-|-|-|-|
|1|6C|6C|6C|
|
|2|8F|6C 8F|8F 8F|
|
|3|52|6C 8F 52|52 52 52|
|
|4|B8|6C 8F 52 B8|B8 B8 B8 B8|
|

**Reporter**: [Zoltan Ivanfi](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=zi) / @zivanfi
#### PRs and other links:
- [GitHub Pull Request #504](https://github.com/apache/parquet-mr/pull/504)

_{**Note**: *This issue was originally created as [PARQUET-1353](https://issues.apache.org/jira/browse/PARQUET-1353). Please see the [migration documentation](https://issues.apache.org/jira/browse/PARQUET-2502) for further details.*}

首先定位 RandomValues 类，并阅读它如何返回其内部缓冲区。查看 Pull Request #504 了解现有工作，然后验证累积的随机值在连续调用之间仍保持不同，并确认相关测试通过。

由索引模型根据 Issue 内容生成。