Make ParquetReader(List<InputFile>, ParquetReadOptions, ReadSupport<T>) constructor public

My application uses s3 storage to store parquet files. The problem is that there is not ability to get rid from `new Configuration(true);` which load configuration from files:
`core-default.xml` and `core-site.xml` every time when ParquetReader instance is created.

I suggest just make ParquetReader(List, ParquetReadOptions, ReadSupport) constructor public then there will be ability to do custom builder.

**Reporter**: [Dmitry Sysolyatin](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=dmsysolyatin)
#### PRs and other links:
- [GitHub Pull Request #707](https://github.com/apache/parquet-mr/pull/707)

_{**Note**: *This issue was originally created as [PARQUET-1719](https://issues.apache.org/jira/browse/PARQUET-1719). Please see the [migration documentation](https://issues.apache.org/jira/browse/PARQUET-2502) for further details.*}

Start at the ParquetReader(List, ParquetReadOptions, ReadSupport) constructor and inspect how the existing builder creates readers. Make the constructor publicly accessible so callers can create a custom builder without the unwanted Configuration loading, then verify the existing reader behavior remains intact.

Scritto dal modello di indicizzazione a partire dal testo della issue.